Alcatraz Island is an island 1.5 miles offshore in San Francisco Bay. The island has a long military history and is now the sight of the Famous abandoned prison.
In the series, Alcatraz is bought by John Dee's company Enoch Enterprises under the pretense of it being turned into a living history museum, which would have worked as a cover story, because Litha, the appointed time for the Dark Elder take-over, would have come before inquiries were made because his masters had given him the task of gathering many dangerous monsters to release upon the city. Perenelle is also imprisoned on the island for a period of time before she managed to escape with the help of the ghost of Juan Manuel de Ayala, the original founder of the island and poltergeist. The sphinx was also there, and to lead her off and away for a short moment, Juan and Perenelle send other ghosts to distract her.