Door

Doors are blocks that are only obtainable through crafting. Upon clicking the object with either the left or right mouse button the block will shift from its native closed state to an open state allowing passage; clicking the door once more will return it to being a closed door.

- Doors can take quite a bit of time to destroy. To destroy them more quickly, simply destroy the block beneath the door.

- In the current version of Infdev destroying the top half of a door will return nothing, simply destroy the lower half to get a door back.

Double Doors
Video reference to placing Double doors here. Depending on what direction you are trying to make your door face (north, south, est or west) you may need to do different steps, like placing the left door first.

Glitches
Possibly due to a glitch in detection, monsters may attack through doors; creepers will detonate, zombies are able to reach through them and skeletons can shoot arrows through them.

Doors may be placed on doors, but it will be lost, and nothing will happen.

There was also a duplication glitch that occurs when a door is placed onto a half step/leaf block/glass block, causing two door drops to spawn where the first door was set down. This was fixed shortly after the update containing doors was released.

They are not available in Indev, if this is intentional or not is unknown to this author.