(covers information from several alternate timelines)
This page contains information regarding new Star Trek material, and thus may contain spoilers.
Alcatraz was a small island in the San Francisco Bay, famous for being the site of a maximum-security prison in the 20th century. On a clear day, the island could be seen from San Francisco's Presidio.
A version of Kathryn Janeway from the year 2404 told her past self in 2378 that one could see Alcatraz from USS Voyager's ready room on a clear day, because Voyager was a museum located on the Presidio in that timeline. (VOY: "Endgame")