Old areas on the Galactica and other battlestars where navigational readings were taken hundreds of yahren prior to the destruction of the Colonies.
Apollo found an unused Celestial Temple, which was housed near one of Galactica's engine. Being the only known Celestial Temple in existence, Apollo repaired it; Celestial Temples were mostly removed from battlestars in the Colonial service, as their use was superceded by advanced technologies.
Celestial Temples were comprised of transparent tylinium and had shutters that could close when not in use. (The Hand of God)