The JLA Secret Sanctuary was a cave in the side of a mountain in Happy Harbor, Rhode Island. Used throughout the Silver Age, the League abandoned it when they moved to the Justice League Satellite. It has since been used by the android Hourman, Young Justice, Doom Patrol and Justice Society of America at various times. Snapper Carr also lived there for a time.
The cave is frequently returned to when the League is in flux, used as a rally point when a more current base of operations is unavailable.
In Other Media
The Sanctuary appears in the premiere episode of the Young Justice animated series, where it is renamed Mount Justice and is stated to have been the Justice League's original headquarters. After Aqualad, Robin, Kid Flash and Superboy declare they will continue to work as a team, Batman provides them with Mount Justice to use as a base of operations under the supervision of Red Tornado and the training of Black Canary, while Batman himself would deploy them on covert missions.