A cave or cavern was a large open underground space.
The Tribe of Gum kept their prisoners in the Cave of Skulls. (TV: An Unearthly Child)
Barbara followed Tegana to the Cave of Five Hundred Eyes while in 13th century China. (TV: Marco Polo)
The Kastrian thermal chambers were a system of caves used by the inhabitants as shelter from solar winds. (TV: The Hand of Fear)
Queen bats were large, hairy bat-like creatures that lived in the caves of Androzani Minor. (TV: The Caves of Androzani)
In the early 19th century, Lord Aldbourne and his followers played at devil worship in the cavern beneath the church at Devil's End. In the 20th century, the cavern was converted into a museum of witchcraft. (PROSE: The Eight Doctors)
Hetocumtek's totem pole was found in the 21st century, hidden deep in a cave in the Mojave Desert. (TV: The Curse of Clyde Langer)
In the far future, A cave was part of the artificial jungle aboard the Ark. The First Doctor, Steven and Dodo hid in the cave from a Monoid. (TV: The Ark)