Nine centuries-old fortresses guard the walls of this medieval Romanian city.

The enchanting archway is the only surviving portal into Dublin's lost medieval wall.

The medieval town's star-shaped walls are geometrically dazzling, though not entirely impenetrable.

Destroyed numerous times, this centuries-old bridge has always been rebuilt with its original design.

Featuring the last fully walkable parapet walkway in Europe.

Rome's ancient Etruscan rival, now a park full of ruins.

Inside this Jewish cemetery is a memorial to soldiers who deserted the German army and were executed.

This sublime architectural marvel is a rare example of an expressionist church.

An artist has turned what most people would consider a bathroom nightmare into a work of political art.

The remains of the observatory of the Danish astronomer who first measured the speed of light.

An ultra-modern diversity park in Denmark has turned an entire city block electric pink.

This ruined 15th-century hermitage is steeped in myth and mystery.

Now nearly dry, this lake is said to be the ancient home of the Lady of the Lake, and was once thought to be bottomless.

The ruins of an 11th-century Norman castle with a rare, perfectly circular shape.

This historic home of the author of Lawrence of Arabia, has a history of literary celebrities and monogrammed sleeping bags.

This antique prison is a tourist attraction with a sordid past.

The eternal resting place of the last highwayman hanged in England.

An oasis of calm, nestled in the English countryside.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

This disused boat elevator was saved from the scrap heap so that visitors could tour its rusting skeleton.

These rustic holiday homes are made from discarded fishing boat hulls.

Underneath a chalk hill in France lies what Hitler hoped would be the underground launching base for a devastating new weapon.

This surprising gem is a world-class archeological museum hidden at the University of Chicago.