This massive subterranean fissure is known as the "underground Grand Canyon."

One of the tallest lighthouses in the world also serves as a monument to the fallen of World War I.

During World War II, this rice mill became a Nazi concentration camp.

This historic stone bridge has an entire neighborhood clinging to its sides.

A sprawling Baroque park with 300-year-old hydro-pneumatic waterworks.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

This medieval castle overlooking the Elzbach river looks just like it did hundreds of years ago.

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

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

The small alleys in Lübeck's Old Town are a result of medieval urban sprawl.

The world's first and only three-segment bascule bridge folds up into the shape of a capital "N" to let boat traffic through.

One of the last remaining railway viaducts equipped with a transporter ferry.

Ample proof that watery ends make for well-preserved, millenia-old mummies.

One of the only Florida forts to remain in the hands of the Union all through the Civil War still stands as a historic stronghold.

Cairns built to bring travelers good luck stretch across the land like miniature stone mountains.

An isolated, rusty phone booth commemorates Iceland's first international telegraph cable.

A formerly glacier-tipped volcano that inspired none other than Jules Verne.

The oldest (maybe) swimming pool in Iceland is a stunning oasis built into the side of a lush hill.

This hobbit-y little hot spring may be the oldest spring used by humans in all of Iceland.

The oldest church in Iceland is one of the few to feature ornate decoration.

These ominous lava formations were said to be an entrance to the netherworld so of course they inspired a famous metal band.

The Icelandic Sea Monster Museum explores the area's history of aquatic cryptid sightings.

This elegant arc of a waterfall marks a religious turning point.

Rising from the sea like a stone monster.