Sylvana

Sylvana was an artificial planet created by the World Builders. It was known as a Hollow World as its interior was a vast Pellucidic cavern. It was illuminated by a sun at its centre, making it a Dyson sphere. A day was roughly 26 hours on Sylvana. Sylvanians were the native life on the planet.

Bernice Summerfield visited Sylvana, having sex with one of its natives, Nialla. (PROSE: Oh No, Not Again)

Sylvana was one of the many planets which fell before Morbius in his war against the Alliance. The Fifth Doctor and his forces eventually took back the planet, and he was reunited with Peri Brown. (PROSE: Warmonger)