Dry Tunnels	Example 1: Dry Tunnel CD	Tunnel map key	-	-
Waterways	Example 2: Waterway ST	Waterway Map Key	-	-
1st Edition AD&D	-	DSG	-	Dragon magazine
<<-- Dragon #130	-	Dragon #131	-	Dragon #132 -->>

Having completed their exploration of
your Dungeoneer’s Survival Guide Underdark
cavern, your adventurers now head
down a 10-mile-long tunnel in search of
the next great cavern. You quickly estimate
the time needed to get through the
tunnel and announce, ?After spending
eight hours marching through the long
tunnel, you arrive . . . ? To which the players
cry, ?What do we find in the tunnel??
? and you discover you have no idea.
Well, don?t despair; the following tunnel
design tables can take care of all complaints
in your underground campaign.

The gigantic Underdark caverns are not
just a few feet apart, so characters actually
spend considerable time moving
through the connecting tunnels. Because
of this, and because well-developed tunnels
add greatly to the overall mood of an
underground adventure, it is important to
design the tunnels well. This is especially
true for beginning Underdark explorers,
who are probably unsure of what equipment
to bring along, what safeguards are
needed, or even what to expect in such a
setting. In fact, in my campaign, the players
had nearly as much fun making their
way down the tunnels as they did in handling
the great cavern complexes!

The following tables can be used to
prepare interesting and challenging tunnels
in any campaign. They incorporate
rules from both the Dungeoneer’s Survival
Guide and Wilderness Survival Guide.
Tunnels are grouped into two categories:
waterways and dry tunnels. The dry tunnels
are traveled on foot, while waterways
can only be traveled by some form of boat.
The dry-tunnel case is examined first,
since dry tunnels are more commonly
used in Underdark campaigns.

Dry tunnels
It is assumed that the DM
has already drawn in the major tunnels
connecting the large underground caverns
of his Underdark realm. To flesh out any
given dry tunnel, one merely needs to
consider that it is composed of one or
more sections ? each with its own set of
characteristics.

There are several ways of using these
tables. One way is to generate each section
of the tunnel; another way is to use the
tables for ideas, and just place cavern
features where desired. (Both methods
have been used in my campaigns.)

For the basic section design, one begins
with Table 1A, which provides the length
of the tunnel section. Next, the section
height and width are found on Table 1B.
Tables 1C and 1D define the section?s slope
and direction, and Tables 1E and 1F provide
the options for the floor surface. The
slopes correspond to the climbing tables in
both the DSG and WSG. Tables 1G and 1H
define local air quality and illumination.

Table 2A is then checked to determine
what, if any, special features occur within
that section. Many of these will provide
numerous challenges for characters and
players alike ? especially for inexperienced
underground adventurers. The
Geothermal Activity table (Table 2B) and
the Section Blockages table (Table 2C) add
variety. But the Habitation Signs table
(Table 2D) can be extremely valuable in
providing subtle clues about the next
major cavern coming up ? dead bodies,
ruined outposts, broken weapons, battlefields,
cairns marking territories, etc.

Lastly, Tables 1I through 1K show what <(1I, 1J, 1K, 1L)>
tunnel changes occur in the next section.
If none occur, this new section can be
incorporated into the preceding section by
simply adding the new length onto the
length of the preceding section. If side
tunnels are needed, one can then use the
tables for designing these branches as
well. The end product is rewarding for the
players and DM alike.

One caution: Don?t be a slave to die rolls.
Some of the choices can be mutually exclusive
or highly improbable. One cannot
have dusty, dry floors and at the same
time have steam vapors in the air, for
condensation would surely form. Further,
one may adjust the design to fit the overall
campaign by including cairns, graves,
broken tools, and the like where desired.
Use of dungeon dressing in Appendix I of
the Dungeon Masters Guide (pages 217-
220) is helpful here.

Waterways
The design of waterways is similarly
handled. Table 3A gives the length of the
section. Tables 3B through 3E yield the <3B, 3C, 3D, 3E>
crucial characteristics needed for travel,
including the section width, water depth,
ceiling height above the water level, and
rate of water flow. Realize that with fast
flow rates come drop-offs ? small rapids
and falls (these are expressed as footnotes
to Table 3E). Tables 3F through 3I give the
section direction, water temperature
(don?t forget hypothermia effects), air
quality, and illumination. The chances for
illumination in a water-filled passage are
low because of the continual water erosion
on all rock surfaces.

Next, add any special features from
Tables 4A through 4D; these are added <4A, 4B, 4C, 4D>
along with any of the drop-offs required
by the DSG flow-rate tables. Again, be
reasonable; if the tunnel is very small and
placid, do not expect to find a whirlpool in
the middle of the tunnel! Lastly, Tables 3J
through 3M determine what aspects (if
any) change in the next section.

I have included two examples of tunnels
fleshed out with these tables. In both
cases, the Underdark caverns are identified
by a letter, such as cavern C. The
major tunnels connecting them are identified
by combining the letters of the caverns.
Thus, tunnel CD connects caverns C
and D. The first example is a dry tunnel
and the second, a waterway.

Example 1: Dry Tunnel CD
General characteristics
Length: 17 miles
Descent: 2,000’
Slope: 2 <2 degrees>
Width: 15’
Height: 15’

Wandering monsters
Check every 6 turns while moving, or
3 times per day while stationary. An
encounter occurs on a roll of 1-2 on ld6.

Special features
Cavern C is home to 76 goblins. The
cavern itself is roughly 300’ x 400’, and
has an uneven ceiling ranging in height
from 25-50’. Cavern D is home to several
normal, underground monsters of neutral
alignment (particularly hook horrors). This
cavern is larger than cavern C, being 400’
x 600’ and having a ceiling ranging in
height from 30-60’. The floor and ceiling
of this cavern are covered by many of the
underground formations listed on page 8
of the DSG (stalactites, stalagmites,
columns, etc.), making cavern D convoluted
in comparison to cavern C.

The tunnel connecting these caverns is
nearly level, dropping almost imperceptibly
downward. It has a rough, wet surface
with many twists and turns. The air quality
is normal, and there is no illumination.

Tunnel map key
1. At ½ mile from C, the floor descends
moderately for the next 40’. There is a
chance of falling (see the DSG, pages 15-
20, and the WSG, pages 33-36). Consider
the floor as dry. A falling character may
attempt to catch himself, if the action is
attempted in time. At the end of this section,
the floor becomes wet and resumes
its gentle descent.
<WSG.33: Climbing>

2. At 2½ miles from C, the tunnel narrows
to a width of 5’ and begins twisting
and snaking for ¼ mile. Somewhere along
this path is a wandering monster; use no
large-sized monsters.

3. At 5 miles from cavern C, there is a
50’-deep chasm. This chasm is 10'-wide
and totally blocks the tunnel. The remains
of a stone bridge are visible. (The goblins
smashed the bridge to prevent intrusion
into cavern C.) On the extremely rocky
floor of the chasm are 112 cp, 253 sp, and
two gems (worth 50 gp and 10 gp). Broken
bits of weapons can be found, along with
pieces of bone from slain goblins and
adventurers. In the northeastern corner of
the chasm is a narrow side tunnel that
runs northward. It is 5’ high and 4’ wide;
its floor is very rocky. If the party decides
to explore this tunnel, it ends after 3 miles
at the edge of a subterranean creek. Further
exploration is possible only by boat.

4. At 6½ miles from C are the skeletons
of three creatures: a duergar and two
goblins. They have been dead for a long
time. A careful study of the area reveals
the signs of a skirmish, and a few bits of
broken weapons litter the floor.

5. At 7½ miles from C is another steep
descent. This one is slightly wet. It is classified
as a “steep downward’ tunnel and is
100’ in length.

6. At 8 miles from C is a large chamber
roughly 50’ x 75’. The entire rough-walled
cavern has been hand-carved. Debris
litters the floor, and there is a large mound
of rock in the southeast corner of the
chamber. A careful inspection of the walls
indicates that a vein of gold runs northwest
to southeast. (The duergar dug this
exploratory chamber while determining
the size and extent of the vein. It is capable
of producing only 10 gp worth of gold
per man-week, which is why the duergar
abandoned the venture.)

7. At 10 miles from C is a series of ledges
on either side of the trail. These are filled
with piles of small boulders. Here, the
goblins intended to bombard invaders and
then retreat.

8. At about 11½ miles from C are three
minor side rooms occupied by wandering
monsters. From here on, the tunnel narrows
to 10’.

9. At 13 miles from C, a large stone cairn
marks the end of goblin territory. Here,
the tunnel widens to 15’ again.

10. At 15 miles from C, the tunnel becomes
very warm for nearly 500’ (geothermal
heat is responsible). There is a side
tunnel running steeply downward for 5
miles, punctuated by numerous twists and
turns. This tunnel is approximately 4’
wide, with an average ceiling height of 3’.
The increasingly hot side tunnel ends in a
partially cooled bed of lava (50’ x 90’).

11. At 15½ miles from C is a 100’ section
of tunnel filled with noxious vapors. Halfway
through this section is a 1” crack in
the wall extending from the floor to the
ceiling. This crack leads eventually to the
same bed of geothermal activity as in area
10. Noxious gas continually sprays from
the crack (see the DSG, page 37). Beyond
50’ on either side of the crack, the vapors
have been diluted enough so that they are
longer harmful.

12. At 16 miles from cavern C, the passage
becomes very windy. As a result of
this, torches are 50% likely to be blown
out each round and cannot be relighted.
Lanterns, if shielded, continue to burn. An
inspection of the ceiling reveals a 2’ circular
shaft rising nearly vertically. The air
rushes up the shaft. The windy condition
lasts for nearly ½ mile, at which point the
party discovers another similar shaft. This
one, however, is in the floor and goes
nearly straight down. The air rushes up
out of this hole. Many miles below is a
large duergar city; together, these two air
shafts are part of the city’s air ventilation
system. If a coin or rock is dropped, no
sound will be heard on landing. The shaft
is miles deep. Beyond the shaft toward
cavern D, the air speed is normal.

If the party attempts to detect odors
here, say that there is a trace of smoke
from something burning and some odors
of cooking.

Example 2: Waterway ST
General characteristics
Length: 3 miles
Width: 20’
Water depth: 6’
Overhead clearance: 4’
Rate of flow: Medium (60’ per round)
Water temperature: 40°F
Air supply: Normal
Illumination: None
Drop-offs: 10% chance of one 1-3’ drop-off
per mile

Wandering monsters
Check every 6 turns while moving, or
3 times per day while stationary. An
encounter occurs on 1-2 on 1d6.

Special features
Cavern S is home to 37 troglodytes. The
stream that constitutes waterway ST enters
this cavern in the east, flows through
the middle of the cavern, and exits to the
west. The stream itself is 20’ wide; a
bridge connects the cavern floors separated
by the waterway. Cavern S is 400’ x
400', with a ceiling height of 25’. The
floors of this cavern are made of water-smoothened
limestone.

At the end of waterway ST is cavern T,
an abandoned duergar mine that has filled
completely with water. The cavern is
roughly 100’ x 200’, with a ceiling height
(from water level) of 15'. The cavern floor
is completely submerged underwater,
although a few ledges and rock escarpments
jut out from the cavern walls. The
water depth in this cavern is 30’ in the
abandoned mine’s center. In the north wall
of the cavern is a tunnel that formerly
served as an exit from the duergar mine.
The tunnel has now collapsed. Though the
tunnel and stream continue to the surface,
there is no room for passage; the water
level reaches the ceiling of the tunnel.

Although the mine has been abandoned,
a few small gold veins have not been completely
tapped. Industrious players may
find a way to extract these metals (worth
100-400 gp), although transporting them to
the surface will be a problem.

Waterway map key
1. At 3,000' from cavern S, the tunnel
width narrows to 10'; the rate of water
flow increases to 120' per round. This
section is 500' long. After 3,000', there is a
series of 3 large boulders in the middle
of the stream; check for collisions.

2. At 1 mile from S, the tunnel resumes
its original width and rate of water flow.
Sandy beaches are on either side for the
next 500'. On the northern beach are signs
of an old campsite.

3. At l½ miles from S, 6 large columns
partially block the tunnel; check for collisions.
For the next 400', the ceiling height
above the water drops to 2'.

4. At 2 miles from S, a side tunnel runs
northward. It is only 5? wide and has a
water depth of 3? and a head clearance of
2?. The tunnel is very twisty and deadends
in 3 miles. At the very end, there is a
small silver vein capable of producing 25
sp worth per man-week, for a total of
1,500 sp.

5. At 2½ miles from S are side ledges on
either side of the tunnel. Both ledges are
covered with flotsam. Various pieces of
broken weapons, clothing, and other gear
can be found in the drift piles. Buried in
the debris is a badly scoured ivory carving
that is worth 100 gp. On the north ledge is
a small monster lair (DM?s choice).

6. At 3 miles from S is a side chamber
that is above water and dry. It is about 20?
x 30?, and is home to a wandering monster
(DM's choice). It has very rough walls
marked by several large cracks. The cavern
shows numerous signs of flooding.
During a flood, water pours into the room
from the cracks. In the northeastern corner
of this small cavern is a tiny ledge
covered by a patch of edible fungi which
has just begun to take hold in the stony
wall. Underneath the fungi patch are the
rotting remains of a leather pack and
clothes. In a pocket of a shirt is a forgotten
earring worth 10 gp.
 

Underdark Tunnel Design Tables

Dry Tunnel Design
General Characteristics Tables 1A-1K

Table 1A
Length of Section

1d20	Distance (dice)
1-2	5-40' (5d8)
3-6	40-90’ (30 + 10d6)
7-11	100-400' (10d4 x 10)
12-18	500-1,000? (400 + (10d6 x 10))
19-20	500-2,000? (10d4 x 50)

Table 1B
Section Height and Width

1d20	Type (height x width)
1	Tiny (1? x 1?)
2	Tight (2? x 2?)
3-4	Crawl (3? x 3?)
5-6	Wide crawl (3? x 5?)
7-9	Very narrow (5? x 3?)
10-13	Narrow (5? x 5?)
14-18	Normal (10? x 10?)
19	Wide (15? x 15?)
20	Very wide (20? x 60?)

Table 1C
Section Slope

1d20	Description (<degrees> slope)
1	Steep up (51-70°)
2-3	Moderate up (31-50°)
4-7	Gentle up (15-30°)
8-13	Level (between 15° up and 15° down)
14-17	Gentle down (15-30°)
18-19	Moderate down (31-50°)
20	Steep down (51-70°)

Table 1D
Section Direction

1d20	Direction
1-3	Curving right
4-6	Curving left
7	Sharp right
8	Sharp left
9-16	Straight
17-20	Twisting and snaking

Table 1E
Floor Texture

1d20	Description
1-2	Slick/polished
3-5	Smooth
6-11	Normal
12-15	Rough
16-17	Tiered
18-19	Covered by large boulders
20	Covered by sharp rocks

Table 1F
Floor Condition

1d20	Description
1	Water-filled (up to 1? deep)
2-6	Slippery (wet and slimy)
7-15	Slick (damp or wet)
16-19	Dry, good footing
20	Dusty (dead tunnel; check cave-in chances)

Table 1G
Air Supply

1d20	Description
1	Poisonous./ noxious gas
2	Stale
3-6	Faint circulation
7-13	Normal
14-16	Drafty (1)
17-18	Windy (2)
19	Rushing air (3)
20	Steam vapors

Table 1H
Illumination*

1d20	Light quality (equivalent to:)
1-10	None
11-14	Very weak light (moonless)
15-17	Weak light (moonlight with overcast clouds)
18-19	Moderate (moonlight with no clouds)
20	Bright light (twilight)

* All underground illumination is assumed
to come from either luminescent
fungi, larvae, insects, or rocks.
Shafts to the surface of the earth
should be extremely rare and would
provide little light. Magical light sources
are always possible.

Table 1I
Changes Following This Section

Step	Section change (table reference)
1	Distance must always be rerolled (Table 1A)
2	Roll the number of attributes that change (Table 1J)
3	Roll for the attribute(s) that change (Table 1K)

Table 1J
Number of Attributes That Change

1d20	Attribute changes
1-5	None
6-10	1 attribute
11-14	2 attributes
15-17	3 attributes
18-19	4 attributes
20	5 attributes

Table 1K
Attributes That Change

1d20	Section change (table reference)
1-4	Section height and width (Table 1B)
5-7	Section slope (Table 1C)
8-11	Section direction (Table 1D)
12-15	Floor texture (Table 1E)
16-17	Floor condition (Table 1F)
18	Air supply (Table 1G)
19	Illumination (Table 1H)
20	Add special feature (Table 2 group)

 Dry Tunnel Design
Special Features Tables 2A-2D

Table 2A
Special Features

1d100	Features
01-30	None
31-36	Side ledges or tiers
37-43	Minor side rooms (3-60? wide x (10d20 x 10)? long)
44-46	Stairs (natural or manmade)
47-53	Side tunnels that dead-end in 1-6 miles with cross sections of 5' x 5' or less (roll 1d100 for special features; 20% are small underground streams)
54-59	Pits (3-18' deep)
60-65	Chasms (20-200? deep x 4-40? wide)
66-70	Cliffs (10-100? high)
71-75	Geothermal activity (Table 2B)
76-84	Blockages (Table 2C)
85-95	Habitation signs (Table 2D)
96-98	Minor mineral vein
99-00	DM's choice

Table 2B
Geothermal Activity

1d20	Description
1-8	Hot or boiling pool of water
9-10	Poisonous/noxious gas vent
11-13	Steam vent
14-19	Hot air
20	Lava pool

Table 2C
Section Blockages

1d20	Blockages
1-3	Large boulder field
4-6	Minor cave-in
7-9	Water pool
10	Quicksand
11	Oil pool
12	Tar pit
13-17	Large stalactites, stalagmites, or columns
18	Balconies
19	Waterway (random size)
20	DM's choice

Table 2D
Habitation Signs

1d100	Signs of habitation
01-05	Cairn marking territory
06	Ruined building (outpost or guardpost)
07-12	Old campsite
13	Small, abandoned shrine
14-15	Dead bodies
16-17	Shallow grave
18-19	Burial mound
20-21	Secret stash
22-35	Broken tools, weapons, or armor
36-37	Intact tools, weapons, or armor
38-41	Battlefield
42-62	Worked stone surfaces
63-70	Abandoned adventurer?s gear
71-89	Intact bridge
90-00	Ruined bridge

Waterway Design
General Characteristics Tables 3A-3M

Table 3A
Length of Section

1d20	Distance (dice)
1-2	5-40' (5d8)
3-6	40-90’ (30 + 10d6)
7-11	100-400' (10d4 x 10)
12-18	500-1,000? (400 + (10d6 x 10))
19-20	500-2,000' (10d4 x 50)

Table 3B
Section Width

5d12	Description
5-20'	Narrow
20-60'	Average

Table 3C
Water Depth

1d10	Depth (at tunnel's center)
1	1' or less
2-3	1-4'
4-6	5-9’
7-9	10'
10	15'

Table 3D
Ceiling Height

1d10 (above water)	Height
1	1' or less
2-3	1-4'
4-8	5'
9-10	10'

Table 3E
Rate of Flow

1d20	Description (flow rate)
1-4	Stagnant (0' per round)
5-9	Placid (1-40' per round)
10-15	Medium (41-120' per round) (Roll of 1-2 on 1d6 results in one drop-off of 1-3' per mile.)
16-19	Rapid (121-240' per round) (Roll of 1-5 on 1d6 results in 1-6 drop-offs of 1-4' per mile.)
20	Cascade (241-600' per round) (3-18 drop-offs of 1d8' each per mile.)

Table 3F
Section Direction

1d36	Direction
1-3	Curving right
4-6	Curving left
7	Sharp right
8	Sharp left
9-16	Straight
17-20	Twisting and snaking

Table 3G
Water Temperature

1d20	Temperature (°F)
1	32°
2-3	33-35°
4-12	36-40°
13-15	41-45°
16-17	46-50°
18	51-80°
19	81-100°
20	100+°

Table 3H
Air Supply

1d20	Description
1	Poison or noxious gas
2	Stale
3-6	Faint circulation
7-13	Normal
14-16	Drafty (1% chance of torch blowout per round)
17-18	Windy (10% chance of torch blowout per round.)
19	Rushing air (50% chance of torch blowout per round)
20	Steam vapors

Table 3I
Illumination*

1d20	Light quality (equivalent to)
1-15	None
16-18	Very weak light (moonless)
19-20	Weak light (moonlight with overcast clouds)

* All underground illumination is assumed to come from either luminescent fungi,
larvae, insects, or rocks. Shafts to the surface of the earth should be extremely rare
and would provide little light. Magical light sources are always possible.

Table 3K
Number of Attributes That Change

1d20	Attribute changes
1-5	None
6-10	1 attribute
11-14	2 attributes
15-17	3 attributes
18-19	4 attributes
20	5 attributes

Table 3L 
Attributes That Change

1d20	Section CHANGE (table references)
1-4	Section width (Table 3M)
5-6	Water depth (Table 3C)
7-8	Ceiling height (Table 3D)
9-12	Rate of flow (Table 3E)
13-16	Section direction (Table 3F)
17	Water temperature (Table 3G)
18	Air supply (Table 3H)
19	Illumination (Table 3I)
20	Add special feature (Table 4 group)

Table 3M
Changes in Section Width

1d6	Width alteration
1	Decrease width by 10' (or 5' if width is currently 10')
2-5	No change
6	Increase width by 10'

 

Table 4B
Geothermal Activity

1d20	Description
1-8	Hot or boiling water
9-10	Poisonous/noxious gas vent
11-14	Steam vent
15-20	Hot air

Table 4D
Habitation Signs

1d100	Signs of habitation
01-10	Cairn marking territory
11-13	Ruined building (outpost or guardpost)
14-25	Old campsite on ledge or beach
26-29	Small abandoned shrine
30-34	Dead bodies, on land or floating
35-36	Shallow grave on land
37	Secret stash
38	Dam
39-41	Canal
42-59	Flotsam or jetsam (broken tools, weapons, armor, or boats)
60-63	Intact tools, weapons, armor, or boats
64-74	Worked stone surfaces
75-80	Abandoned adventurer's gear
81-00	DM's choice

MARCH 1988