Portal
- link: https://store.steampowered.com/app/400/Portal/
- category: 3D action game
- release year: 2007
- developer: Valve
- publisher: Valve
- description:
- The spaces between two portals are connected.
- For example, if you open one portal on the floor and the other on the ceiling, then drop an object into the floor portal, the object will fall infinitely.