The abandoned remains of this once-thriving hotel looms over the city, awaiting an uncertain future.

The world's second largest single-dish radio telescope, once used to contact E.T.

This limestone cave offers an incredible view of the Río Grande de Arecibo valley.

Legend tells how a Spanish soldier disappeared from this isolated sentry box without a trace.

A magnificent waterfall nestled in the heart of the El Yunque National Forest.

A sharply wedged sundial marks the point at which each day in the United States begins.

This huge pile of volcanic boulders hides a stunning network of secret grottoes.

Rusting, graffiti-covered tanks litter the beach of this island, once used by the U.S. military for target practice.

Rumored to be the famed pirate's lookout tower, this historic stone structure is now just watching for tourists.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

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

A 19th century hat factory still stands as a crumbling ruin in upstate New York.

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

A once grand hotel is being retaken by the wilderness it once capitalized on.

The lost town of Neversink, sunk by New York City.

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

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

A reversed traffic signal that was once violently misinterpreted as a statement on British-Irish relations.

A tiny islet just off Long Island offers a wealth of infectious curiosities.

A tribute to the hard-working men and women of Grumman, who crafted F-14 fighter jets.

An abandoned Gold Coast-era mansion once intended for the exiled ruler of Albania, who never arrived.

A historic lighthouse steeped in rumors of ghost and pirate stories.

A millionaire's abandoned swimming pool from the gilded age of one of America's most distinguished families.

An eccentric playboy's astounding natural history collection.