A fiery crater has been burning in the Karakum Desert since 1971.

You can row a boat through this ancient underground reservoir.

This vertical pinnacle in China was the inspiration for the floating mountains in the movie “Avatar.”

Two ancient Buddhist temples crown this dramatic rocky pinnacle.

Isolated atop this Balinese sea crag is a lovely Hindu temple that is said to be guarded by sea snakes.

An unfinished tomb carved into a giant boulder in the Arabian Desert.

This scenic fortress dates back at least 2,400 years to the time of Magna Graecia.

This hill and tower are steeped in legend, from King Arthur to the Holy Grail.

This foreboding medieval castle was twice besieged by barons rebelling against the English king.

The birthplace of the ferocious William the Conqueror, this castle is awash in medieval history.

This Norman castle has been the scene of assassination plots, religious persecution, and Nazi conspiracies throughout its long history.

A spiral staircase twists to the top of this unusual Czech lookout tower.

The ruins of a medieval monastery named after a type of tree.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

This 15th-century Serbian Orthodox monastery also contained a school for illuminating manuscripts.

This outcropping was once home to a medieval monastery destroyed during the Ottoman conquest.

Artists have long been drawn to these atmospheric 12th-century ruins.

This Gothic castle-like portal is a testament to the amazing craftsmanship of the navvies who built the railway tunnel.

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

This picturesque castle in Poland has a rich history, including a legend that ties it to lost Incan treasures.

Picturesque ruins once held off mighty armies.

This Scottish castle has witnessed clan rivalries, Jacobite uprisings, whisky smuggling, and more.

The ruins of a Roman fort lie in the shadows of an imposing medieval castle.

One of the most well-preserved castles in Italy also contains a rare medieval example of a port fortification.