A character can achieve the ethereal state by various means which include magical ointment (oil of etherealness),
magical items, magic spells and psionic discipline.
It is possible to move to or about any plane which the Ethereal Plane permeates,
and it is also possible to move from plane to plane ethereally.

All movement and travel in the Ethereal Plane is subiect to certain hazards.
Some monsters are able to function partially in this plane.
Some monsters roam freely in the Ethereal Plane.
The worst hazard, however, is the ether cyclone,
a strong moving force which can cause the individual to enter a different world or plane or become lost in the ether for many,
many days when it blows across the stretches of this multi-plane.

Ethereal travel is tireless and rapid.
Creatures in ethereal state need neither food, drink, rest, or sleep.

Your referee has complete tables for encounters in the Ethereal Plane as well as for movement of the ether cyclone and its results.