'Hollow Earth' is a belief that the planet Earth has a hollow interior and, possibly, a habitable inner surface.

Mystara is a hollow planet, with a habitable surface on its interior called the Hollow World.

We can inspect the ring's habitable surface to some extent as it diminishes below us.

An approximately equal number of tanks and similar machines had disappeared along with the habitable surface of Prairie.

Why bury all that painfully extracted matter inside your habitable surface?

But that only means the moon's not habitable on its unprotected surface.

Will only move on habitable surface.

A geologist conducts readers through the dynamic past of the planet and its constant reshuffling of the habitable surface.

Things would be easier for the men if they were picked up there instead of having to get back down to the habitable surface on their own.

"Are we to explore the habitable surface of the ring?"