This network of roads is one of the most unique Etruscan creations ever discovered.

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

This small hermitage is located along an ancient route that connected the Tiber and Rieti valleys.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

Now overgrown, these anti-tank barriers from World War II are sometimes called "dragon's teeth."

This hermitage spanning an Italian river gorge draws pilgrims hoping to heal ailments like arthritis and migraines.

This human-made pond is part of a Korean palace complex first built in the 7th century.

The cave where Saint Genadio meditated and played chess.

Hidden in a high mountain cave, this hermitage dates back to the ninth century.

A beautiful chapel on the hills of the Oltrepò Pavese claims to house the tomb of King Edward II of England.

This brothel-turned-restaurant features plenty of surprises and elaborate, extravagant architecture.

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

A Victorian Gothic masterpiece housing a world-class collection of rare books and manuscripts.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

An imperial church bombed to ruins during WWII now stands as a jagged memorial.

A book bound in the skin of an infamous criminal, along with countless other specimens.

This Buddhist temple is home to the graves of the Japanese national legends, the 47 Ronin.

Underneath this small church are 15,000 bones, arranged by an obsessive academic.

This modern French ossuary contains the jumbled bones of 130,000 WWI soldiers.

Poland's oldest salt mine has nearly everything one needs to live underground forever.

The Buddhist temples of Yamadera, built into a mountain side, feature a viewing deck with sweeping views.

This abandoned asylum in Wales might look haunted, but it's still beautiful.

Hundreds of stone stairs and a winding medieval bridge connect this haunting Spanish island to the mainland.

A spiral staircase connects the limestone cave with Pembroke Castle, birthplace of King Henry VII.