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

A small museum along the Susquehanna River is home to a rich collection of Native American artifacts.

For decades, it has disappeared and reappeared as water levels rise and fall.

This picturesque stream was up until recently the site of a ten story mountain of slag and sewage.

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

Behold the rickety wooden glory of the world's oldest operating roller coaster.

The pop art icon's gravesite is broadcast 24 hours a day on his museum's website.

It would take 35 firetrucks to fill this enormous glacial pothole.

This public space is speckled with the eerie remnants of a defunct amusement park.

The internal railway of one of the biggest steel plants in America has been transformed into a linear park with unique industrial views.

This Old Testament garden features 100 plants from biblical times.

A train station that was abandoned by the coal industry and was later converted into a cocktail bar.

The universally beloved children's television figure is interred on a high hilltop in one of western Pennsylvania's oldest cemeteries.

This eerily well-preserved coal town was saved from destruction by a Sean Connery movie.

A modern ghost town whose inhabitants were driven away by the growth of nuclear power.

A stone arch leads to a cavernous 1930s spring house tucked away in the Pennsylvania woods.

An abandoned stretch of highway, deteriorating next to the operational one.

Mysterious rocks that ring musically when struck.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

Collection of trolley cars in the woods represent one man's attempt to preserve transportation history.

Mussolini gave Cincinnati a bronze statue of Romulus and Remus suckling at a wolf's teats.

Abandoned since the 1950s, the streetcar lane beneath the heavily trafficked bridge lays empty and unused.

The ruins of the suspension bridge hang over Kingsbury Run as a ghost of racial prejudice.

An unoccupied lighthouse encased in layers of ice from the waters of Lake Erie.