This abandoned Croatian stronghold never saw a great deal of conflict but it is still a beloved relic nonetheless.

The European towns of Brașov and Râșnov each have proud signs reminiscent of the Hollywood sign.

A marvel of Byzantine engineering under the streets of Istanbul.

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

This ancient subterranean megalopolis is known for the hot oil traps that were installed above each of its entrances.

While not Turkey's deepest underground city, this subterranean redoubt is the largest.

This centuries-old tree tells an unusual tale of vegetation and fertility in the desert.

Skyscraper powered by wind turbines attached between its towers.

This beautifully historic Bahrain fortress might not be the most popular attraction around, but that might make it all the better.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

Yemen's "Stone Palace" looks like it was carved right out of the tall stone column on which it is built.

These warring psychedelic crags commemorate an unsuccessful military operation.

An Ethiopian "Jerusalem" featuring a church hewn out of a single rock.

Holy Hindu shrine in an enormous, monkey-filled limestone cavern.

5,000 skulls in memorial to those killed by the Khmer Rouge.

Khmer Rouge's high security prison.

A battle between nature and architecture in the Cambodian jungle.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

The Habsburgs' royal collections of art and wonders.

The mummified right fist of a 1,000-year-old saint-king sits inside an ornate golden reliquary.

Budapest's Communist-era statues, banished to the suburbs.

An ancient knight and a symbol of the city's freedom.

A towering spire in the fortress of Kalemegdan honors the victorious armies of Serbia during their struggles against the Ottoman Empire.

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.