No one really knows how these old hobby horses got here, but the herd keeps growing.

A tunnel once abandoned now thrives with graffiti art as an off-limits makeshift gallery.

A crumbling staircase in upper Manhattan is all that remains of one of the most important sites in sports history.

Collect holy water from a Bronx grotto.

Hidden inside one of the world's most well-visited zoos is a secret plaque promising eternal life.

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

This plot of old-growth forest is the largest surviving remnant of New York City's original woodland.

Every year model trains zip through a miniature New York City that's now 150 landmarks strong.

An unassuming stone building houses New York City's oldest seismic station almost 30 feet below the Bronx.

The first "Hall of Fame" in America was designed by legendary Gilded Age architect Stanford White for what was then the NYU uptown campus.

Small monoliths of several varieties of stone sit alongside a wooded path in the Bronx.

A large boulder marks the place where the island of Manhattan was purportedly "sold" to the Dutch.

This derelict building used to house infirm Freemasons, their widows, and orphans.

Series of storm drains connected to a dark urban legend.

Seven golden statues rise into the sky from sculptor Victor Victori's New Jersey front lawn.

An abandoned horticulture institute gloomily presides over rows of derelict and vine-wrought greenhouses.

This once-grand marvel of engineering is now 41 miles of scenic hiking trail.

America's greatest forgotten garden and the former stomping grounds of Son of Sam.

Self-sufficient greenhouse floating on the Hudson River.

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

A trash dump made beautiful by nature's power.

A house built from trash known as the poor man's Hearst Castle.

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

A New York garbage depot holds a secret collection of weird and wonderful refuse.