The beautiful tunnel that ran from the lobby to Penn Station is still hidden underneath 34th Street.

Discovered by cows, these upstate New York show caves are presented with a healthy dose of psychedelic folk art.

The railroad tunnel nicknamed the "Bloody Pit" for taking the lives of hundreds during its construction.

This mysterious artificial cave has long puzzled New Englanders.

Ruins of the elaborate house where the enigmatic costume designer threw glamorous parties for New York's theatrical elite.

The ruins of a Massachusetts prison farm can still be found crumbling the woods of a state park.

The only surviving building of historic West Boylston, which was flooded to create the Wachusett Reservoir.

This railroad tunnel was once the longest in Massachusetts.

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

The former locus of Boston's high culture has been shuttered and buried for over 70 years.

Unlike other abandoned asylums this empty institution welcomes visitors, just don't go in the buildings.

An elaborate, hidden model train in the Needham Town Forest.

Once the largest public hospital for the mentally ill was also surrounded by controversy.

This headstone-like marker inscribed with three words has been an utter mystery for over a century.

One of the now-less-hidden floral gems of the "Emerald Necklace."

Ralph Waldo Emerson spent two years living here decades before it became a Frederick Law Olmsted-designed park.

A beautiful Victorian-era cemetery, complete with a miniature village.

The ruins of one of the first railroads in the U.S. lie hidden within a neighborhood cul-de-sac.

Plans for this peninsula included houses, the United Nations Headquarters, and a nuclear power plant. When none of them worked out, it became an expansive park.