Venice's island of the dead.

On rare days, this abandoned castle's gatekeepers open its doors, revealing the eye-popping splendor hidden inside.

Medieval town turned hippie commune, once home to the secret foreskin of Jesus Christ.

Stalactites and stalagmites in a beautifully lit cave.

This Venice bookstore has resigned itself to constant flooding by keeping its books in bathtubs and boats.

Abandoned medieval hill town.

Hidden in an Italian forest is a completely homemade amusement park that has taken a lifetime to create.

Nightmarish example of the unintended consequences of weapons testing.

Villas that once served as playgrounds for the rich now fall away in decay.

This abandoned mining village was predicted to resist decay longer than any other modern human settlement.

Terrifying derelict military hospital once housed a recuperating Hitler.

When German-Iraqi relations broke down, this embassy was vacated post haste.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Morocco's Argania trees are infested with nut-hungry goats.

Founded as a refugee camp, now a popular tourist spot.

This former steel and coal plant is now a neon-lit industrial fantasia.

The world's biggest pet store.

This small town in the Netherlands has no roads but instead, miles of canals and over 100 bridges.

The Bloemen Route, or “Flower Route”, stretches 25 miles through prime Dutch tulip country as a result of “tulip mania,” the world’s first economic bubble.

Colorful and chaotic stacked hotel in North Holland.

Cat art as far as the eye can see.

What almost started out as a spite house became an eccentric's found object masterpiece.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.