If you close a door on yourself, you can climb the door by jumping up and standing on the bottom block of the door, then jumping again to land on top of the door.
Steps to reproduce:
- Stand in the spot where the door will be when it closes.
- Close the door.
- If you're in the right area, you'll be able to walk through the door to either side.
- Jump straight up.
- You'll land in the door, standing on the bottom half of the door.
- Jump straight up again.
- You'll be standing on top of the door.