An open-air sewer system that was covered piece-by-piece over 300 years.

The patron of this extravagant Art Nouveau confection insisted that nothing less than a boat should project from its facade.

A dramatic art installation features a BMW flying out of a building in Rotterdam.

Each time a baby is born in Ghent, these streetlights flash in silent celebration.

This fairytale castle was built as a show of power but was nearly torn down thanks to its history of torture.

The sumptuous ceiling was one of the last things Charles I saw before his execution.

The 2,000-year-old beam is tucked within the pedestrian entrance to the old London Bridge.

A wonderfully eclectic Victorian aquarium lies in the basement of the Horniman Museum.

Following the trail of an old metro line, this scenic path is haunted by a creepy spriggan statue.

In this cobwebbed old operating theater, you can practically hear the screams of the unanesthetized patients.

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

The fences outside some of South London's estates are made from recycled World War II stretchers.

The relics are stored in a silver reliquary, where they can be seen through glass.

A mysterious emblem tucked in an small alleyway is actually the coat of arms of a heroic medieval family.

Polish luminaries and masterful folk art find sanctuary in this unique cemetery.

Countless stories attempt to explain Poland's mysterious J-shaped trees.

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

Artfully arranged bones of 5,800 Austrians.

This former insane asylum now holds a pathological anatomy museum.

Beautiful Austrian natural history museum with carved ceilings and row after row of ancient taxidermy.

The beautiful baroque library of the Hapsburg empire.

A silly medieval mural preserved on the side of a Viennese house.

Apartment complexes built into huge repurposed natural gas tanks.

Tucked away near more famous landmarks lies a statue meant to symbolize the confluence and continuing development of human culture.