Bunker SF-Zero-One was a bunker operated by Starfleet located under Starfleet Headquarters.
History and specifics
Bunker SF-Zero-One had duplicate systems for all of Starfleet's command systems. It was built hundreds of years ago, possibly before the founding of the Federation.
In the year 2375, Captain Jean-Luc Picard led a group of newly graduated ensigns into this bunker to coordinate the defense of Earth when the Breen Confederacy attacked San Francisco. (TNG - Tales of the Dominion War short story: "Eleven Hours Out")