These caves secretly held national treasures during World War II.

This mystical orb covered in strange symbols is thought to have been used in ancient Greek magical rituals.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

An ancient octagonal weather station named for the eight Greek gods of wind.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The martyr's wax-enhanced skeletal remains lie preserved in a glass case in the Santa Maria della Vittoria in Rome.

This Cambodian riverbed is covered in ancient Hindu carvings both above and below the waters.

A battle between nature and architecture in the Cambodian jungle.

5,000 skulls in memorial to those killed by the Khmer Rouge.

Thousands of bats stream out of caves every night on the edge on Thailand's second largest park.

Monkeys lounge around at this 13th century temple.

The largest and best-preserved Roman amphitheater in Africa was designed to seat 35,000 people.

Made famous by 'Star Wars,' these troglodyte homes face an uncertain future.

Buildings from the fictional planet of Tatooine still litter the Tunisian desert.

The ancient heart of Tunis is an enormous maze of narrow streets and alleyways.

The world's most active stratovolcano is almost always erupting.

A dismembered holy head stares out from her beautiful reliquary at the St. Dominic Basilica.

Italian cave with exceptional acoustics and an unsavory history.

A monument hidden in the woods built in 1938 as a getaway for a Dutch museum curator.

The place where houses are born.