On a bit of a nostalgia trip from recovering an old poem, I recalled an old dungeon that I helped design with a friend back in middle school. It was a bit of a fun-house with all sorts of crazy gimmicks. One of these gimmicks was an area submerged under "liquid oxygen" (or more correctly, an oxygen-rich liquid that air-breathers could survive in). I imagine the puzzle facing the characters as they try to navigate the area since it wouldn't radiate magic and actual water breathing spells or potions would be wasted. How would they determine that they could breathe? There could be clues or the characters could just make the discovery by accident.
Anyway, this geomorph has a submerged area (noted by the light-gray shading) that may be breathable liquid or it might just be water. The arrows point down the slope of the three ramps and there is a large room in the east that may be the source of the liquid (a balcony overlooks a submerged fountain). The well or pool in the small room to the southwest may or may not be related to the submerged areas.
Go Ape with 5e
1 hour ago