Erath
From Tardis Wiki, the free Doctor Who reference
The Lost Planet of Erath inside the Great Park RealSpace, which could only be reached via a specific series of hyperjumps. The planet had incredibly strong defenses. The reason for this was twofold, both that there was a colony of robots that served as aspects of the Universal Machine that lived here, and that inside the planet the Downtime Gate rested. (PROSE: Of the City of the Saved...)