An illusory pile of treasure (**true sight** and similar negates) conceals a pressure plate which, when pressed, erects a 5 ft square glass box. The glass chamber's floor is made of coal and sulfur and catches fire, dealing 1d4 damage each minute for the first 10 minutes, then 2d4 for a minute. In the meantime, the room around this box floods with water. The room takes only 10 minutes to fill. Once it is full, the water spills through cracks in the doors, releasing the doors so the players can leave with only 1d12 suffocation damage (underwater breathers are immune). The water also causes the glass box to crack open, freeing the cooking player.
Smoke swirl liquid and black by Chuttersnap. Unsplash License.