Once America's longest-manned military fort, now an abandoned hulk.

An abandoned subway tunnel that could have reinvigorated Staten Island still lies somewhere beneath this Brooklyn park.

The abandoned husk of a mental institution that failed to save a Jazz Age icon still sits nearly unchanged.

This abandoned ironworks was once the most important military supplier in America.

This abandoned factory on the Hudson River once churned out a million bricks a week.

A former connection to City Island, it has been abandoned since the 1930s.

A forgotten relic from New York's bygone trolley system hides in plain sight under a bridge.

The remains of what was once the world's steepest passenger funicular.

Buffalo's abandoned concrete grain elevators are getting a second life.

A spooky and decrepit mental health facility is slowly being replaced with newer digs.

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

This statue commemorates the importance of hat manufacturing to Danbury, once known as the "Hat City of the World."

An abandoned asylum where patients have been forgotten but their possessions remain.

This abandoned psychiatric hospital once housed more than 4,000 patients in the middle of a quaint New England town.

These World War I shooting range tunnels are now haunted halls of underground graffiti accessed through the roots of a tree.