Geography: The placid river flowing from Area 17 gradually
picks up speed until it reaches the shaft shown on the map. Here
it plunges 2,000 feet straight down, finally splashing into the deep
subterranean lake that makes up Area 30. The shaft the water
plunges down is 100 feet in diameter. Just before the water
plunges over the fall, it passes a sturdy breakwater and landing.
At this point, travelers can remove boats from the water and walk
along a wide trail that follows the river into the shaft. The trail
becomes a long series of wide stairs cut into the rock opposite the
waterfall, and the stairs switchback down the entire length of the
shaft. At the bottom, they terminate in another landing adjacent
to the lake.
The lake itself fills many adjoining caverns. Some of them are
completely filled, making boat travel impossible, but in most
areas the ceiling rises 20 feet or more from the surface of the
lake. A wide, placid river slowly makes its way out of the lake to
the south, and a more aggressive current carries water into a
large cavern to the north of the lake, where the whirlpool is
located.
The lake’s depth varies from cavern to cavern, but it is rarely
shallower than 100 feet. In some places, the bottom is 1,000 feet
below the surface.

Denizens: As might be expected, both the kuo-toa and the
aboleth wander these caves, although neither race maintains
dwellings here. They are often on the watch for intruders from the
Plane of Water, who gain access to the Prime Plane through the
whirlpool.

A number of monsters roam the deep waters of these caverns,
using the wide river leading to Area 31 as a means of infesting
that area as well. These aquatic carnivores include giant catfish,
giant gar, scrags (marine trolls), lampreys, merrow (aquatic
ogres), giant sea snapping turtles, and giant pike. The marine
trolls and ogres maintain lairs in small caverns along the sides of
the lake, while the other monsters constantly roam about in
search of prey.

A small group of nymphs resides in these caverns. They live in
caves half-filled with water, very close to the waterfall that spills
into this area. They jealously guard against intrusion and strive
constantly to keep the water pure.
The large cavern containing the interplanar whirlpool is
claimed by a host of creatures from the Elemental Plane of Water.
An assortment of nereid perpetually guards the approaches to
the cave. If intruders approach, some of the nereid attempt to
keep them at bay while others hasten to their own plane to return
with reinforcements. These arrive three turns after the intrusion
is discovered.

Creatures from the Plane of Water who answer the nereids’
calls for hetp include water elementals, water weirds, tritons, vardig,
and marid. Unless the incursion is a major one, only one or
two types of these creatures respond at a given time.

Resources: The water is clean and plentiful. The air does not
circulate well, but few of the creatures here breathe it, so characters
have no shortage. The caves of the ogres and trolls contain
limited amounts of treasure, but little else of value can be found
here.

Unique Features: The whirlpool cavern is an elemental vortex
like the mud and lava vortices in Areas 29 and 21. Characters
must be able to breathe water in order to survive a journey to the
Plane of Water. In addition, the guardians from that plane must
either be defeated or persuaded that the characters serve a
cause that they support. A few of these creatures, such as tritons,
lean towards good alignment.