The stairs led into a natural cavern below the house.

They entered another cavern, this one natural and larger than the first by several times.

At the tunnel's end was a system of natural caverns deep beneath the surface.

Just above ground level where there are three natural caverns, one after the other?

They stood in a natural rocky cavern with dim light.

Plus there is some air supply available from natural caverns, deeper under the Earth.

The shrine had been built in an enormous natural cavern.

Looking around she saw a chamber that was a large and apparently natural cavern.

There was a large, natural cavern within the canyon walls that served as a home for all.

It is a natural cavern which has been changed into a shrine.