The Airlock is a door that allows colonists to enter and exit a bio dome. Placement of airlocks is an important consideration when creating your base to ensure colonists can get about the planet efficiently. It's usually a good idea to have space bike posts near to an airlock so the bike travels less distance to pick up a colonist that has just used the airlock to get outside. Airlocks can be damaged an destroyed, which will trap colonists inside the base.