A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

The eerie remnants of an ancient forest were hidden under the sand for centuries.

One in a pair of subterranean caves created by an ancient eruption of Mount Fuji.

This granite rock face is named for the magnificent reflection that occurs when the sun hits it just right.

A grove of "candelabra redwoods" deep in California's Lost Coast.

This ancient stone bridge dates back to the early Middle Ages.

This tangled English forest looks like something right out of a fairytale.

These medieval tunnels provided water to the city above through centuries of civil war and plague.

The weathered grave of a medieval anchoress who walled herself up in a cell attached to a church.

In a sleepy village in Oxfordshire, the visionary English writer's gravesite attracts a yearly pilgrimage.

These brass bunnies honor the rabbits that dominated the no-man's-land around the Berlin Wall.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

These former Nazi anti-aircraft towers offer a singular view of the north of Berlin in the summer, and a sanctuary for bats in winter.

The lost ruins of the forgotten ferry lie hidden beneath the silt.

"The Donut" was built as part of an expensive, ill-fated engineering endeavor.

The colorful stairs are made with marble from the world's major quarries.

This Alamo Square mansion is rumored to have hosted satanic rituals and other occult practices.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

The site of the climactic scene from the classic horror film is now a historic landmark.

Quite simply the largest tree in the world (by volume).

Dating back almost 400 years, the oldest public collection library in the United Kingdom was once the study hall of Karl Marx.

The housing complex served as an anti-fascist fortress during the Austrian Civil War.

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.