An absolutely beautiful 200-foot stained glass installation traces the evolution of knowledge.

This dramatic landscape hidden on the Isle of Skye looks as though you've stepped into the magical realm.

An abandoned jewel of a ballroom on the top floor of Australia’s busiest rail station echoes with the sounds of a bygone era.

Lima’s Museum of Anthropology is lined with thousands of elongated human craniums.

Think you have a tough job? Try carrying 200 kilos through a cloud of sulfur down the side of a volcano.

This cavernous swimming spot doubles as a home to the largest known colony of bats in Central Asia.

Ancient barriers wrap around what was once an important stop along the Silk Road.

A fiery crater has been burning in the Karakum Desert since 1971.

A catapult rock from Gotland’s 13th-century civil war is still lodged in Scandinavia's best-preserved medieval city wall.

A sinister pyramid in the Frari contains the heart of the famous neoclassical sculptor.

Originally a leper colony, the island is now an Armenian monastery that's home to an incredible manuscript library and eclectic museum.

Venice's island of the dead.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

This ancient trail climbs the mountain where a Latin League cult worshipped Jupiter, its main deity.

An abandoned 17th-century baroque hunting lodge with a wonderfully strange architectural plan.

The ruins of a thousand-year-old hermitage are tucked away deep in the sloping forests of Albano Lake.

The underground sanctuary of a mysterious ancient cult.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

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

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

Hidden in a grotto 26 feet below Nottingham's oldest hotel, this stylish subterranean drinking den is notoriously hard to find.

This ancient tunnel is one of the most important examples of Roman hydraulic engineering in Spain.

In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

The Neapolitan Cult of the Dead still cares for the skulls at this mini-Fontanelle.