Planet (Underworld)

A planet formed by the gravitational pull of debris floating through a spiral nebula assembled into a nearly hollow planet around the hull of the ancient Minyan spaceship called the P7E. It was once visited by the crew and passengers of the R1C.

The planet's interior resembled a series of caverns and caves, and it had an atmosphere breathable by humanoids. Despite its rocky interior, it was a soft planet in the process of being formed. Thus, when the R1C — crewed by near-immortals, who had extended their lives by regeneration — crashed into it, the R1C was relatively undamaged.

This crew — along with the the Fourth Doctor and his companions K9 and Leela — not only survived the crash but explored the planet soon thereafter. When the Doctor and Leela first stepped onto the planet, he called it "the Underworld", referencing its similarity to a place in Greek myth. There, they found the descendants of the original P7E crew, who had lived their lives enslaved to the computer known as the Oracle. These inhabitants — Guards, "Trogs", and Seers alike — knew nothing of their origins, let alone that nuclear war had destroyed their original homeworld.

After the defeat of the Oracle, the "Trogs" boarded the R1C, bound for a new planet, Minyos II. (TV: Underworld)