Juiblex's Swamp is a special level in Gehennom that is covered with water. It is located between the 4th and 7th levels of Gehennom (and therefore on DL 29-36). Juiblex, a slug-like demon lord, lurks there (unless already summoned by a chaotic sacrifice). Juiblex's Swamp is eligible to leave bones files. The entire level is no-teleport. You can dig down through the floor, but you will have trouble with water filling your pit (even with a wand of digging).