Minecraft wiki entry for Trapdoor_uses, associated text: Trapdoors can be used to create a door which cannot be entered by mobs but is convenient for the player to enter on foot or in a minecart. This is done by placing a closed trapdoor on the upper block inside a 1*2 doorway and a minecart track under it leading through the door. The player is not affected by the trapdoor, and the minecart travels on the block under it, so the player can ride a minecart through the trapdoor without getting hurt and without losing speed.