One of Philadelphia's largest murals resides hidden under this bridge.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Suspended above the ground in a thicket of towering Georgia trees is a modern architectural wonder.

Secret gardens just a few miles from downtown Atlanta.

The largest cemetery in the American Southeast is a hidden gem near the heart of Atlanta.

A beautiful, dense forest in the shadow of Mount Fuji, with a tragic reputation.

A 20-meter (65-foot) robot towers over Tokyo Bay.

A taste of the macabre Tokyo's ritzy shopping district.

Thirty creepy ghosts now inhabit this decaying 14th-century church.

An abandoned NSA listening post on Berlin's "Devil's Mountain."

Abandoned Nazi train station turned underground astroparticle laboratory.

An abandoned concrete jungle surrounded by a lush park.

This abandoned prison castle has become an imposing gallery of graffiti art.

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

The Denver airport is guarded by a 32-foot-tall sculpture of a demonic horse.

This former tuberculosis research hospital endeavored to cure the dreaded disease with fresh air and positive attitudes.

The now-abandoned tunnels were built for the transcontinental railroad on the route where the first wagon train entered California.

An abandoned relic of the city's failed experiment with below ground transit.

A hidden alley in urban Baltimore is a haven for graffiti artists.

Atlanta's strange assortment of concrete pillars inspires reflection in some, confusion in others.

This derelict superstructure was a very important warning system for the Soviet military.

Once the most densely populated place in the world, this island is now a ghost town.

Not quite the menace it once was, this monster still has some chops.

This Detroit ruin was once a gothic bastion of its community, but now it stands as a haunting ruin.