Gaseous Grotto

Long ago, the exceedingly wealthy Lord Iben Drakhm needed a number of relics retrieved from different locations on the Elemental plane of Air. He carefully selected the most talented adventurers among his subjects for the mission. But only weeks before they set out, it became evident that they were not experienced in dealing with the different environments they would most certainly encounter. So, the mission was postponed, and an expensive training facility was constructed so the adventureres could learn how to tackle a variety of challenges different gases will pose. Thus, no expenses were spared and the Gaseous Grotto was constructed.

The grotto consists of five challenges, and the individual rooms are separated by water locks. Each chamber has a tiny one way portal to the Elemental Plane of Air, where gas of a specific kind constantly leaks in, filling the room. Anyone inside must either hold their breath of begin suffocating immediately.

1. Hydrogen, low density and very flammable and explosive. Six skeletons haunt this room, waiting for living visitors they can tear apart.
2. Cholorine, highly poisonous. Anyone with skin exposed to this atmosphere must every round save vs. DC 25 or take 20 HP and d3 CON damage. A successful save deals 10 hp damage, but no stat damage. One large and one medium air elemental resides here, guarding a diamond they once captured from a Xorn they slew.
3. Oxygen, very flammable and explosive. Normal humanoids can breathe here, but only for CON number of rounds. After that, breathing inflicts d2 points of temporary WIS and INT damage each round. A djinn is trapped here, and she is eager to escape.
4. Argon, causes inert gas asphyxiation (treat as suffocation). Two invisible stalkers have taken up residence here. They enjoy playing cards and dislike interruptions, but may let others join if they show aptitude for the game.
5. Helium, low density, causes inert gas asphyxiation. Five dust mephits camp out here. They serve the djinn trapped in room 3, but are unable to reach her.

All air elementals in the grotto are hydro-phobic and thus trapped inside their chambers. The skeletons in room 1 could theoretically swim to room 2, but lack the imagination.