The Last Home of an Executed King.

Holy Grotto of Montserrat Monastery holds one of Europe's mysterious black Madonnas.

A miniature train-ride through Slovenia's largest cave system.

This modern French ossuary contains the jumbled bones of 130,000 WWI soldiers.

The fairy tale castle of the "fairy-tale king."

Fascinating town where normal life interfaces with the occult.

The biggest and deepest Cold War bunker open to the public can be found in southeast England.

Scattered throughout London are ancient remnants of the city's former bounding wall.

Unusual British home built to disguise a water tower.

A village on the east coast of England that has almost completely eroded into the North Sea.

A marvel of Byzantine engineering under the streets of Istanbul.

Roman ruins top white travertine terraces formed by ancient hot springs.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

Mausoleum and Holy Seat of Antiochus I of Commagene.

Roman ruins, natural methane fires and a lovely beach.

Huge winged monument in the United Kingdom.

Seat of the Duke and Duchess of Devonshire for centuries.

6000-year-old site covered in more than 50 megaliths.

The National Railway Museum in York is the largest railway museum in the world, attracting almost 1 million visitors per year.

Astonishing rock formations dot the Brimham Moor landscape.

Standing in a state of "arrested decay," this ghost town allows for a detailed peek into Gold Rush life in an unusually harsh climate.

The rocks in this arid basin leave trails of movement behind them.

Macabre astrological automaton clock dating to the late 1400s.

A church of bones, decorated with 40,000 human skeletons.