The entire base had been built in a gigantic mountain cavern.

I've read some science-fiction books about aircraft landing in concealed mountain caverns, but that's not a strong probability.

There is a substance called Wraithstone, a chalky white material found in certain remote mountain caverns.

Older children led younger ones into the mountain caverns, which were unsealed to receive them.

They turned and moved silently from the ammunition room toward the single exit from the mountain cavern.

The mountain caverns crawl with the little beasts, and the only thing that keeps them in there is their own stupidity and fear.

And so at last he came to the mountain cavern accompanied by thousands of mares.

The world was vastly altered: for instead of a mountain cavern and rough stone altar, she stood alone in the centre of a low-ceilinged room.

Yes, much darker, like mountain caverns, and rimmed with eruptions of silver.

Krishna's companions, the cowherd boys, entered its mouth, mistaking it for a mountain cavern.