From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

Marked by the hand of the explorer Henry Morton Stanley.

This 17th-century structure is a beautiful testimony to traditional Persian architecture

Named after a legendary garden called Eram in southern Arabia, built by order of Shaddad, an Arab king who wanted to compete with Paradise.

A dreamy mausoleum honors Persia's most famous poet.

This ancient burial site is believed to be one of the first earthquake-protected structures in the world.

These little castles each held thousands of pigeons.

17th century mosque for Shah Abbas' harem.

The ancient necropolis houses the immense rock-cut tombs of four Persian kings.

A spectacular rainbow of stained glass makes the "Pink Mosque" one of the most beautiful in Iran.

The palace of the King of Kings, burned by Alexander the Great.

The ancient heart of Tunis is an enormous maze of narrow streets and alleyways.

St. Mary's features one of the most spectacularly decorated cathedral interiors in all of Europe.

Real bones which are said to have belonged to a Polish dragon.

An underground city of salt.

A striking memorial to the Jews of Leiden who were murdered during World War II is scattered throughout the city.

A massive explosion that leveled hundreds of buildings in the city of Leiden is remembered by a waterside plaque.

This 11th-century castle sits so low you can't see it behind the surrounding buildings.

This hotel was once home to a steamliner company and became the final rest stop for Europeans heading to the New World.

The Netherlands' first car tunnel has an unusually rectangular shape.

An unassuming rod in the Netherlands was once the old standard unit of length for the entire Dutch empire.

Now a museum, this building was once a 14th-century monastery and the place where the founder of the Dutch nation lived and was assassinated.

People have been placing babies on these lilies for photoshoots since the Victorian era.