There's plenty of unique accommodation in the world, whether it's up among the trees, set precariously on a cliffside or built to imitate a film set. But some of the most surprising places where you can stay the night aren't above ground at all.

Whether they're deep in disused mines, carved out of rocky cliffsides or squeezed into claustrophobic caverns, click through this gallery to discover Earth's most astonishing underground stays...