Heavy Door (Portal 2)
The heavy door is found in the Behind the Scenes sections of Portal 2.
To add a door, the easiest method is to create a func_instance with the VMF file instances/door/vertical_security_door.vmf.
For a simple door that opens when approached, create a brush overlapping the door, link to trigger_playerteam, and add these outputs:
You can use other types of trigger (e.g. a logic relay, a button) to control when the door opens.
Use the dropdown to explore other parameters; there are fast and close opens as well as a malfunctioning open.
An easy way to make the door one-way is to put your trigger on only one side of the door.