A corroded metal chest lies on a grate on the far side of the room. Green liquid flows from several holed on the wall and drips onto the chest, which then drains through the grate.
|The green liquid is toxic and naturally flows into the space behind the wall, which then drains out through the holes.
A DC 14 Intelligence (Nature) check identifies the green liquid as toxic and caustic when inhaled or contact of any sort is made.
All targets that start their turn within 10 feet of the liquid must make a DC 14 Constitution check or take 1d2 Constitution damage.
Creatures that touch the liquid must make this save at disadvantage.
The holes can be easily plugged, as the liquid is not super viscous. Once the holes are plugged, the toxic effect stop in 1d2 rounds as the liquid drains down the grate.
However, 1d4+1 rounds after the last liquid drains, the liquid behind the wall builds up enough pressure to burst through the wall. When this happens, all creatures in the room take 2d6 bludgeoning damage, with a DC 12 Dexterity saving throw halving this damage.
In addition, any creature that takes damage immediately takes 1d2 Constitution damage. The liquid stays on them until an action is taken to scrape it off.
Once the wall is destroyed, there is no way to stop the liquid flow into the room.
The chest is a normal iron chest that can be opened with a DC 12 Dexterity check with thieves’ tools.