A derelict bit of transportation infrastructure hidden in the woods.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

This forgotten building was one of the few Philadelphia-area breweries to survive Prohibition.

An eight-sided home built during a brief octagon craze in the 1850s.

An Industrial Revolution-era public work that purified water using nothing but sand.

An abandoned railroad tunnel forgotten by time awaits inquisitive hikers.

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

Once the world's largest reinforced concrete structure, this abandoned bridge now beckons urban explorers.

An eerie, decaying ghost town destined to fade into the forest.

An overgrown garden stands as a grim marker of an unrealized dream.

Now abandoned, the first public health hospital in the U.S. saw more than one million immigrants from around the world.

This abandoned, windowless concrete block is one of the strangest buildings in Tulsa.

These abandoned grain silos and tunnels are an urban exploration dream.

A forgotten Cold War relic hidden in the outskirts of a Wisconsin city.

A hidden piece of Altoona's railroad history in a long-forgotten abandoned town.

The ruined remains of a coal mining ghost town are hidden within the woods.

This dam in the woods, built by Henry Ford with only manpower and oxen, holds no water and serves no purpose.

This isolated airport in the middle of the Everglades sees more alligators than planes.

This off-the-beaten-path abandoned town is a relic of Montana's silver mining boom.

This abandoned bridge to nowhere stands secluded in the woods of a Cleveland suburb.

Ruins of a historic medical facility sits eerily by the water.

An enormous overgrown greenhouse teeming with graffiti and wildlife.

An abandoned car and strange wooden debris are among the scattered remains of the old sand and gravel quarry.

A little-visited ghost town state park offers a glimpse into Montana’s "Silver Queen."