Trapdoor

The Trapdoor (also known as Hatch) is a block used as a horizontal door that fills one block space. It was introduced in Beta 1.6.

They can be placed anywhere with a solid block directly adjacent. When activated, they will then open by flipping upwards toward the adjacent block. If that block is destroyed, the trapdoor will break off into a resource. Due to this restriction it is currently not possible to create a flat floor with a trapdoor opening downwards.

When placed outside, rainfall, water and snowfall do not pass through a trapdoor, but light is allowed to shine through.

Usage
As with Doors, Trapdoors can be controlled with Redstone circuitry. Redstone in its charged state will cause the trapdoor open. Conversely, redstone in its uncharged state will close the trapdoor.

Trapdoors can be used as a less unsightly method of restraining boats at a dock than doors.

It's also possible to create a distributor with a vertical succession of trapdoor linked with redstone.

They can also be used to create gates, since they stop horizontal movement as well. Similarly, they can be used to create a gate for a countertop (such as can be found in a bar or restaurant).

See Tutorials/Trapdoor Uses for Tutorials/Examples.

Bugs

 * Trapdoors block movement when approaching from another block on the same level and the trapdoor has a block exactly 2 spaces above it, but it does not block movement in the same case if approaching from another trapdoor, or if you are approaching the trapdoor from a space that is also 2 blocks high. This allows one way drawbridges.
 * If there is a ladder beneath a trapdoor, you can climb down, if you are standing on the ladder through the trapdoor, even if the trapdoor is closed.
 * Trapdoor textures are mirrored incorrectly.
 * When the block that a trapdoor is attached to is powered by a repeater, the trapdoor will only work if the block it is attached to also has redstone or a redstone torch attached to it. (the same applies to doors as well)
 * If a trapdoor is placed diagonally to another trapdoor, you will sometimes fall through if walked over.
 * Liquids (water and lava) cannot fall through a single or a 2x2 hole trapdoor. The trapdoor counts as a block and can't have something else in it, even in its open state. Trapdoors will stop the block above it whether it's open or closed.

Trivia

 * Sand and Gravel, if dropped onto a trapdoor will break into items (similar to how sand or gravel falling on a torch will do the same).
 * When attached above a block of lava, lava will still put the adjacent blocks on fire. This makes trapdoors unsuitable as disposal lids.
 * Trapdoors will not prevent you from accessing the contents of a chest if the trapdoor is in the closed state directly above it. This means that they are just like any other Door and allow you to interact with objects on the other side even if the trapdoor is closed.
 * If you put a trapdoor on a lava block, the lava will disappear and the trapdoor will not be burned. This allows the creation of paths.
 * Trapdoors can be used as ladders by placing them one above each other down a hole. Then from hit them open to go down, and hit them close to go back up.
 * The trapdoor as a dropped resource is much bigger than other resources.
 * Trapdoors can be used as fuel in a furnace but burn only as much as a wooden plank.
 * Trapdoors can be pushed by pistons if there's another block for it to connect to or if the block it is currently connected to is pushed with it.