New Alexandria was a lifeless planet on the edge of the Capricorn Tract and orbiting a neutron star. It hosted a domed complex containing the Crystal Bucephalus and the hotel that surrounded it, the Emerald Syphax. It was surrounded by the Time Vortex. (PROSE: The Crystal Bucephalus)
Behind the scenes
It is strongly implied that New Alexandria is built on the ruins of Gallifrey, with Kamelion even beginning to say that the planets have the same coordinates before being interrupted. (PROSE: The Crystal Bucephalus)