Miles of man-made caves and tunnels are currently used for cultivating mushrooms.

The great Italian Renaissance painter was laid to rest here in the Chapel of Saint-Hubert.

This museum preserves over-the-top masterpieces that once qualified artisans for membership into a medieval guild.

Limestone grottoes turns everyday objects into stone.

Discovered by cows, these upstate New York show caves are presented with a healthy dose of psychedelic folk art.

A hands-off space for graffiti artists to hone and display their skills.

Grotto replete with mystical designs laid out in glued shell mosaics.

Man-made cave with enigmatic carvings, some say made by the Knights Templar themselves.