Trapdoor

The trapdoor is a new block type implemented in the beta 1.6 update.

They are intended to be placed over a single-block hole (but can be placed over a block as well) 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 is as well. Just like doors, trapdoors can be activated by redstone. When placed outside, rain, water and snow fall do not pass through a trapdoor.

Crafting
When crafted with six wooden planks, two trapdoors are created. Video

Uses
-Drawbridge: If you place the trapdoors in a trench in this fashion:

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t=tdoor x=block You can create a fairly good drawbrige. You can extend it lengthways, but not widthways. However, it's possible to walk on the ledge of an opened trapdoor if there is enough space above it.

You can also attach redstone to automate it.

Bugs
Trapdoors seem to break faster using a pickaxe instead of an axe, like wooden slabs.

Trivia
Much like the Piston is based on a mod developed by Hippoplatimus, the hatch is very likely based on a mod from DJoslin. (http://www.djoslin.info/trapdoor.php) Trapdoors may not be placed next to double half blocks. 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). Liquids (water and lava) cannot fall through a single hole trapdoor. The trapdoor counts as a block and can't have something else in it, even in it's open state. Liquids will stop the block above it whether it's open or closed.