An Air Lock is an excellent device for quarantining dangerous areas to prevent monster escape, and is very easy to build. It can be handy to have around a Nether Portal or monster farm.
- Two (2) Iron Doors
- Four (4) Buttons
- A minimum of 28 blocks (Obsidian is sturdiest, but Cobblestone is much cheaper)
- First, place one door at the entrance to the room you're trying to quarantine. Surround it with blocks.
- Second, build a corridor between the first door and the second door.
- Third, place the second door at the end of this corridor.
- Fourth, place the buttons in easily accessible places to open and close the doors from either side.
- Fifth, test your air lock. The second door should not be open while the first one is and should not be opened until all unwanted mobs in the quarantined room or the air lock corridor are exterminated.