Ultraworld was an artificial planet with the living heart of a vast brain-like organism called the Core. According to its custodians, the Ultra, the planet "built itself", possessing consciousness and self-awareness and "alive by any meaningful definition of the word".
The planet was located in a quadrant of space where nothing was listed on the star charts, not even a Federation beacon and was never a transit lane for Federation ships. Nothing lived on the outside surface of the planet but underneath, through a network of tunnels. Spacecraft could be brought into a docking bay via one of the pyramids opening, as it did with the Liberator.
The planet's outward look, made of combination of pyramids, gave a threatening and startling appearance with Tarrant exclaiming "what the hell is that?" and Dayna stating she didn't like the look of it. The reflection exterior appearance was able to mentally control Cally.
Shielded by an unspecified means preventing all radiation leakage, the planet was first detected through reflections off its surface as a signal "regular enough to be a pulsar". It had no electro magnetic spectrum which was highly unusual.
Germanium circuitry, recognised by Avon, was as an integral component of Ultraworld. Maintenance required a labour force of menials, described by Tarrant as "walking dead", and the remains of captured individuals who had undergone transference were either used as such menials or fed into the Core. Tarrant was intended by the Ultra to become such a menial. Orac's destabilisation of the Core apparently led to the destruction of Ultraworld. (TV: Ultraworld)