Trapdoor Mat
When the trapped door is opened, a trapdoor in the floor in front of the door falls open. Any creatures within 5 feet of the door must make a DC 12 Dexterity saving throw of fall 20 feet into Area 10. A character can make a DC 16 Intelligence (Investigation) check to discover the trap, and a DC 18 Dexterity (thieves’ tools) check to disable it.