Mount Justice is the base of operations of Young Justice. It is located in Happy Harbor, Rhode Island. Mount Justice was originally the headquarters of the Justice League. The Cave is the interior of the whole mountain, which was hollowed out and reinforced by Superman and Green Lantern during the early days of the League. However, when the secret location of the cave was compromised, they moved to the more public Hall of Justice.
The base was recommissioned in order to house Young Justice. Red Tornado agreed to live in the cave to look after them, and both Superboy and Miss Martian live in the cave as well. Despite the location of the cave being compromised, at current, the team is in no danger of an attack, since whomever obtained the information is aware that the League found out about it, leaving the group to "hide in plain sight", as Kid Flash described it