No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Every equinox this Maya pyramid puts on a spooky ancient light show.

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.

A flooded Mexican cave that hides a river beneath the water.

A Lovecraftian altar of nightmarish bronze chairs sits ominously on a boardwalk in Puerto Vallarta.

The last physical evidence of the Lewis and Clark trail is one of their autographs etched into this giant rock.

A Building for Your (Former) Funerary Needs.

Erotic art covers the walls of the largest ancient pleasure palace.

Rare karst landscape eroded from a flat seabed.

Medicinal spa created with the discharge from a geothermal energy plant.

This stunning concert hall has become a symbol of Iceland's national recovery.

A museum dedicated to the history and exploration of both popular music and science fiction.

A rocky sea serpent hides caves, blowholes, and a spectacular natural bridge.

A modest stone circle in North Wales.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

Ancient snack bar of the Roman Empire re-opened.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

Jesus' footprints and the first catacombs in the world.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

Go inside to really appreciate this 500-year-old technological masterpiece.

100 year tradition of fist fights, marked by marble footsteps.

These medieval skyscrapers dominate the skyline of this small Tuscan town.

Medieval torture techniques with a modern conscience.