Airspace of fly-by monsters and birdmen.
The cavern ceiling is 180 feet above the Crustvein's Classic Forest, and 510 feet above the surface of the lake in the Hellgob.
From either the cliff in the classic forest or out of a hole in the wind cave, there are three points a flying character could reach without fatigue: the elephant sorcerer lake, the slain-bodies field, or a small tunnel entrance to the poison maze.
The airspace is patrolled by occasional solitary harpies and lesser gargoyles. If they take any damage from a flier or spellcaster whatsoever, they will scream, hoping something else will notice and kill the offender (5 in 6 chance of attracting an aggressor from the elephant lake, rolled on the lake's "additional encounters" table). The flier will then retreat to a convenient hex in the elephant sorcerer lake which has cover (the wrecked shacks in the west island if there is nowhere better).
There is a one in 20 chance that a flier encountered in this airspace has a wand of lightning with 66 charges.