This artificial cave looks like something out of a fairytale.

This German bone house contains the remains of some 20,000 souls.

Floating swimming pool within a moored vessel.

A striking 12th-century-style castle built on the edge of a cliff.

A peculiar family mausoleum built by a German nobleman captivated by the occult.

This 700-year-old structure is one of the most unique architectural and historic monuments in Gdańsk.

Warsaw's fantastically preserved gasworks...almost.

The site of the first battle of World War II.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

Also known as the Blue Church, the building was consecrated to the daughter of Andrew II.

A line of disused military bunkers built to defend against Nazi invasion lies hidden on the outskirts of the city.

A cableway for car transport.

An extraordinary museum devoted to the pop art legend created by Slovak artists.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

The world's newest astronomical clock is also its most accurate.

This spaceship sculpture in the middle of the Slovakian capital looks like it just crash-landed.

A perfectly preserved hill village where the buildings are painted like white lace.

The 700-year-old fortress was the site of Count Orlok's castle in "Nosferatu."

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

The house that took a plunge into the facade of a museum.

This "mathematical tower" was an observatory, early skyscraper, and place to reflect on all of nature and the cosmos.

Inside the corridors of this flea market, visitors are sure to find some obscure and odd treasures.

Ugly 18th-century dwarf statues living in a perfectly landscaped Austrian garden.