Guardian of Forever

The Guardian of Forever is a special encounter in Fallout 2, a reference to the Star Trek episode The City on the Edge of Forever. It's a big time portal which lets you travel back in time before the time of the first Fallout to break the water chip in Vault 13. Just like most other special encounters, it is not considered a canon part of the Fallout setting. However, its linear completion provides palpable benefits to the player character.