Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

A wondrous old library overlooking the nation's capital.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

A tiny theater hidden in an alley plays a constant stream of short silent films for anyone willing to peer through the peephole.

Tucked in the back of this amazing antique store is an important piece of medical history.

A crumbling hospital from the 1850s on Roosevelt Island.

This abandoned seaside fortress is now simply an imposing ruin being taken back by nature.

A Natural History and Science Emporium.

First a horse rendering plant, then a 19th century landfill, this beach is full of glass from thousands upon thousands of broken bottles.

A discreet little stairway on St. Nicholas Avenue leads to a quaint and unexpected cobblestone street of 19th century wooden rowhouses.

Mysterious 500-year-old tapestries depict a unicorn hunt.

Harlem park dedicated to compulsive hoarders killed by their own junk.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

Home to the infamous "Typhoid Mary" and the worst loss of life in New York's history prior to September 11, 2001.

Despite not growing anywhere near New York City, bananas are ripened in a pressurized room in the Bronx using precise banana science.

The Vatican of the movie industry turned into an actual church.

Read between the lines of the subway map to find the hidden abandoned Civil War fort.

This outpost of America's most popular fast-food restaurant is housed inside a palatial mansion.

A hyper-luxurious, 12,000- square foot home might be buried beneath Queens, still waiting to protect you from nuclear missiles.