This 13th century Gothic brick castle is the largest in the world by surface area.

A well preserved medieval fortress in Vojvodina.

Also known as Rye Castle, this 13th-century fortification later became a prison and held one of Rye's most famous criminals.

This castle resides in a valley known for immense bloodshed during the Middle Ages.

The abandoned ruins of a beautiful medieval castle just outside Barcelona.

Henry VIII's forgotten castle was built by the gunpowder-obsessed king to be defended solely by cannons.

The soulless eyes of 82 bronze children stare on forever in remembrance of a horrifying World War II massacre.

The 14th-century ruins are said to contain healing powers.

The oldest surviving mosque in the UAE has mysterious origins and unusual architecture.

The United Arab Emirates's biggest and oldest fort pays homage to a lost era.

This abandoned Soviet circus is slowly being restored to its Communist-era glory.

Accessible only by boat, this centuries-old island fort never saw troops or combat.

Tucked away on an empty wooded lot in suburban Oklahoma City lie the remnants of an abandoned circus camp.

A desert ghost town—occupied for only 12 years—was once home to more than 500 silver mines.

Bootleggers ran booze beneath this building before (and after) Route 66 appeared beside it.

The future of roadside attractions is this sci-fi soda mecca that is home to a 66-foot tall neon pop bottle.

A ruined castle has more than its fair share of legends and ghost stories.

A tiny Greek Orthodox church from the Ottoman era hides on a busy city street.

Volcanically heated hot springs.

Hidden in the highlands of Guatemala, a small shrine venerates a forbidden folk saint.

Macabre symbols of death and mummies on display set the tone of this Italian purgatory church.

Geometry and mystery come together in an epic show of octagonal masonry.

The sunlight passing through the opening of this huge cave system creates a magical effect.

Its look is severe, but its location, isolated on a hill in the middle of the countryside, is particularly scenic.