A small island dotted with old, historic Finnish buildings.

On a small island, a replica of a Finnish village from the Iron Age.

One of the oldest structures in Helsinki is this burrow grave that dates back to the Bronze Age.

These large stone piles are ancient burial sites.

A replica of the home of a famous fictional troll family.

Monuments don't get much more metal than these three giant viking swords planted in a Nordic hill.

A reconstructed farm shows what life was like in Norway 1,500 years ago.

An intricately carved Viking church overlooks a glistening fjord.

The largest cave in Northern Europe.

A collection documenting Nazi occupation of Norway, including a painting believed to be made by Hitler.

Each year melting snow turns these Austrian hiking trails into scuba zones.

This open-air museum filled with 19th-century buildings offers a unique view of historic craftsmanship.

This beautiful Croatian fortress is haunted by legends of forbidden love.

Yugoslavia's biggest underground airport lies in ruins.

One of 200 religious buildings recognized as a “culture monument.” 

The largest Roman amphitheater in the Balkans once held over 20,000 people, but managed to lay hidden for hundreds of years.

Formerly Yugoslavia's "forbidden island," this sleepy little city still holds the abandoned remains of military strongholds.

An abandoned monastery sits on a far-off island in the Adriatic Sea.

This Tibetan monastery has survived multiple attacks and is also a sky burial site.

The small cliffside monastery known as the Tiger's Nest is said to be the meditation site of an 8th-century Buddhist master.

The largest and, arguably, most scenic fortress in Bhutan.

Spectacular mineral formations fill these caves, which have been used for everything from smoking meat to stashing illicit liquor.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

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