Door Mimics are recurring enemies in The Legend of Zelda series. They resemble normal dungeon doors, but if Link approaches them, they fall down, crushing him. A variety of weapons, including bombs can blast them off.
Ocarina of Time
Navi doesn't give him a warning about the Door Mimic. Door Mimics only appear in the Fire Temple, Gerudo Training Ground and Spirit Temple. Opening or attacking it will fall down if Link's standing in front of it. A Bomb or Megaton Hammer can destroy it, as he learns from the rescued Goron in the Fire Temple.
Door Mimics never appear on the Dungeon Map as they're fake.
The Minish Cap
Door Mimics are found only in Dark Hyrule Castle and Royal Valley and never resemble the ones in Ocarina of Time. Approaching it will fall with a slight delay, leaving Link just just enough time to step aside. Instead of being a magical one, it seems to be sort of a mechanical trap. After it fell, a chain can be seen pulling it back in position. As with any other versions, a Bomb can destroy it.
There's a glitch in the Fire Temple, if Link hits the Door Mimic by the fire columns, it will fall and doesn't damage him.