Vanguard Atlantis is the name of the undersea facility in the City of Heroes MMO used by the United Nations global security division known as Vanguard mostly for detention of the most dangerous criminals.
It is believed that the facility was once used by the Fifth Column as a staging area after World War II, and then as a storage facility by the Council. Eventually abandoned, it was re-purposed by Statesman and Positron as the perfect place for the Vanguard to keep Rikti prisoners of high importance during the 2002 Rikti Invasion.
After the Invasion, the facility became the ultimate "Supermax" prison for international prisoners.
Located at the bottom of international waters, the Atlantis facility is under no jurisdiction outside of the United Nations Security Council. The only rules they adhere to are those under the Geneva Convention. Access is allowed only through Vanguard bases, mostly through teleporters. The facility does have some submarines for emergencies, but automated defenses prevent any other vessel from approaching the area.
The supervillain Destitution was sent here when it was revealed that he was still alive and was regenerating from his near-fatal injuries.