The blood-soaked ruins of the castle where the murderous Blood Countess was walled in alive.

Abandoned ship reimagined as a street art canvas.

The stately remains of Llywelyn the Great's mighty fortress.

The only medieval bridge in Britain with its defensive tower still in tact.

This well-preserved Cistercian Abbey in a romantic pastoral setting has inspired artists like the poet Wordsworth.

Abandoned waterpark turned counter-culture mecca.

This giant wooden treehouse within a sprawling garden has its own eatery.

A science fiction-inspired apartment building designed by a famous Spanish architect.

A riverside park built around the ruins of a massive dam that collapsed in 1909.

This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.

The ruins stand as a somber reminder of France’s worst civil catastrophe of the 20th century.

The forgotten remnants of a land-to-sea cable car that was once unique in the world.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

This grand stone tower was dedicated to a famed American humorist almost by coincidence.

The superstar of Cold War nuclear bunkers has been featured in countless films but is now barely operational.

Graffiti-covered ruins that were once part of a farm owned by a mental hospital.

The abandoned remains of this once-thriving hotel looms over the city, awaiting an uncertain future.

The 19th-century ruins hide deep in an overgrown forest.

Abandoned in 2009, this once popular resort destination now stands frozen in time.

The ruined remains of the airport Claus von Stauffenberg departed in his failed attempt to kill Adolf Hitler.

For six months of the year, three giant mirrors direct a pool of sunshine onto this otherwise occluded town.

Home of the International Space Hall of Fame.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

Rome's semi-secret peephole vista is also a former Crusader stronghold.