Palace of Paroxysmus

In Ultima Online, the Palace of Paroxysmus is found in the central Lost Lands, just northwest of Papua.

Description
The many slimes at the entrance to this cave already warn what's coming. The so-called palace is actually a cave filled with a river of toxic, poisonous slime, mixed with acid. It also is filled with the minions of Paroxysmus, a daemon of considerable power. If one is persistent anough, it is possible to find him and challenge him ot a duel, in the hope of breaking his hold over this part of the world.

Trivia

 * In order to gain entry into the Palace of Paroxysmus, must you must have an Acid Proof Rope in your bag.
 * Strangely enough, even though Paroxysmus is a demon prince, the demon slayer type does not appear to work on him.