This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

Giant marble phalluses on the sacred island of antiquity.

A Bronze age settlement on the Greek island of Santorini might have been the inspiration for Plato's Atlantis.

This legendary city has been a tourist attraction for centuries.

Hidden in a secluded Greek cove is a pristine beach marred only by the rusting smuggler's hulk stranded on its shores.

The hallucinogenic center of the ancient world.

Monasteries on rock pillars, once accessible only by frayed ropes.

A cake-themed art installation tucked away in historic Chinatown.

Perhaps the most beautiful of preserved saints, with a little help from Paris.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

This enormous sinkhole hides a secret world created from divine wrath.

Countless grotesque faces stare out from this eerie Prague art wall.

This large, circular tomb is the final resting place of the first emperor of Rome.

This Irish show cave is said to have been the site of a Viking massacre that claimed 1,000 lives.

According to legend, this boat-shaped henge is built over the grave of a mythic king.

An intricately carved Viking church overlooks a glistening fjord.

A small etching on the white marble parapet was written in runic script by a Viking mercenary.

An otherworldly, fossil-rich cobble beach holds Viking graves, cairns, and other remains.

A masterpiece of LGBT art has been restored in what may now be the most valuable restroom in America.

It was an experiment to prove that glacial boulders and rocks can be used in constructions and dwelling.

This otherwise ordinary close on the Royal Mile constituted the end of the world for Edinburgh’s poorest residents.

Venice's "Island of the Mad."

A small island less than half a mile from Venice is a forbidden island with a dark and twisted past.

A cheeky reminder about the value of art dangles above one of Olomouc's busiest streets.