An abandoned 14th-century castle and prison complex on a small island in the Neva River.

Abandoned Nazi train station turned underground astroparticle laboratory.

Once the world's largest reinforced concrete structure, this abandoned bridge now beckons urban explorers.

This shell of a historic manor house on the Isle of Wight is said to be the most haunted site on the island.

The wooden house where the jazz great learned to play the piano.

A Viking-style brewpub named for a Norse sea giant, in the heart of fjord country.

A hill carving of the legendary dragon that terrorized the village of Bures in the Middle Ages.

The mummified heart of a saint lives on in this church—after a brief hiatus when it was stolen.

The evocative ruins of a 1,000-year-old hill fort lie within a popular tiger reserve.

This remarkably well-preserved Incan city managed to survive the conquistadores.

A rare example of an octagonal Catholic church.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

An ethereal glowing blue ocean cave in Croatia.

This ruined fortress was the stronghold for a persecuted medieval leader and his infamous Assassins.

This 17th-century mausoleum is topped with an acoustic marvel.

The medieval castle built as headquarters for the Pope's secretive Knights Templar.

An unusual abandoned church damaged in World War II sits in a small village outside Moscow.

A 1,500-year-old, 3-story subterranean city where ancient Persians took refuge in times of war.

In a city that boasts four separate inclined cable railways, this is one of the busiest funicular lines in the world.

The ruins of a monumental tower in the heart of Lebanese mountains still puzzle archeologists.

A fire once nearly devoured this gorgeous 14th-century Gothic cathedral.

15 monolithic temples emulate an eroding sand castle.

An abandoned stretch of highway, deteriorating next to the operational one.

Remains of an abandoned coral city.