The Delphi Union High School in a suburb of Delphi City on Caprica.
It survived the Cylon nuclear holocaust remarkably well and became a base of operations for the anti-Cylon resistance movement led by Samuel Anders, as the Cylons did not run patrols through the area it is located in. Over 100 people at one time lived and operated out of the bombed out High School and it provided good cover from the Cylons, who never once attacked it (although the resistance would be reduced down to 53 by the time Starbuck and Helo met them roughly 46 days after the Cylon attack). For recreational purposes, Anders and his teammates from the Caprica Buccaneers constructed a make-shift Pyramid court in the school's courtyard for anyone who wished to use it ("Resistance").
Nine months after the Cylon occupation began, according to Anders the Cylons had found this location and attacked the base, killing half his remaining men. It is unknown whether or not the school had survived the assault. ("Lay Down Your Burdens, Part I")
Notes
According to a deleted scene aired in the recap at the beginning of the episode "Scar", it is located 300 klicks (187.5 miles) north of the only Cylon airbase in the area; presumably this means the airbase in Delphi itself that Helo and Caprica-Sharon tried to infiltrate in the episode "Colonial Day".