The Cold War-era "underground Pentagon" is a sprawling subterranean hideaway for the Defense Department.

Where America's first doomsday cult awaited the end of the world.

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

This burial mound is said to be the final resting place of Russia's first Viking ruler, Oleg of Novogrod.

Stunning examples of Russia's 18th-century wooden architecture.

Monastery, army base, and infamous Soviet Gulag in the far Russian north.

No one knows why ancient labyrinths were built on this tiny northern island.

Home to three historic ships from the age of Vikings.

This handsomely carved wooden church is more than 800 years old.

Mysterious man-made rock piles form an ancient cemetery on this rocky beach in Norway.

This striking royal residence is the largest Renaissance-style castle in Scandinavia.

Located in the middle of public park, this cave built in the early 19th century houses an ancient stone sarcophagus.

The hidden lair of an alchemist rediscovered in a 2002 flood.

Macabre astrological automaton clock dating to the late 1400s.

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

Originally envisioned by King Ludwig II to rival Versailles, Herrenchiemsee's "New Palace" remains half-gilded for lack of funds.

American soldiers discovered Europe's best one-liner at the end of World War II.

Soaring over 6,000 feet in the Bavarian Alps, this beer garden was once Hitler's 50th birthday present.

The history of occult science is turned into a creepshow at this lurid Prague tourist attraction.

A sculpture of the iconic East German car on four legs is a tribute to those who traveled to Prague seeking asylum.

The oldest garden in Prague, once part of an medieval orchard.

A collection of anatomical samples from one of the first anthropologists to suggest that humans reached North America by crossing the Bering Strait.

Buried five stories underground, this Soviet bunker is packed with gas masks and Cold War paraphernalia.

Housed in an old church, this hunting museum holds a collection of mythical bird-rabbit creatures.