Xanathar's Guide to Everything
Simple Trap, Dangerous (5th–10th Level)
Anyone who steps on the mosaic causes fire to erupt from it. Those who openly wear holy symbols of Pyremius don't trigger this trap.
Trigger. The temple of Pyremius, a god of fire, is threatened by thieves who seek to steal the fire opals displayed there by the priests in tribute to their god. A mosaic on the floor of the entryway to the inner sanctum delivers a fiery rebuke to intruders.
Effect. A 15-foot cube of fire erupts, covering the pressure plate and the area around it. Each creature in the area must make a DC 15 Dexterity Saving Throw, taking 24 (7d6) fire damage on a failed save, or half as much damage on a successful one
Countermeasures. A successful DC 15 Wisdom (Perception) Test reveals the presence of ash and faint burn marks in the area affected by this trap. A successful DC 15 Intelligence (Religion) check enables a creature to destroy the trap by defacing a key rune on the perimeter of the mosaic that is within reach; failing this check causes the trap to activate. A successful Dispel Magic (DC 15) cast on the runes destroys the trap.