A stone arch leads to a cavernous 1930s spring house tucked away in the Pennsylvania woods.

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

This rugged area of red rocks and arches is often considered one of the most beautiful places on Earth.

A castle built by an eccentric medieval enthusiast in rural Ohio.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

When ecosystems collide in the arid Southwest.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

Carved by a waterfall in a hard-to-reach rock formation, this heart-shaped rock has inspired romantics for decades.

In the middle of an extremely unforgiving and desolate high desert is the most secret military facility in the world.

The highest bridge in America was built for an almost unnervingly small amount of money.

A sculpture made of 10 Cadillacs as a monument to the "Golden Age" of the American automobile.

A tiny red pebble marks what may be the quietest outdoor spot in the United States.

An enormous park-like oasis, full of famous Chicagoans' graves.

This road in the Great Smoky Mountains was supposed to assuage a displaced community, but ended up a $52 million dead end.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

See massive fossils that are over 200 million years old in northeastern Arizona.

New York City's smallest piece of private property.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

There is no trying to fall in love with this Star Wars fountain, you just do or do not.

One of only two commuter aerial tramways in the United States.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

The world's longest known cave system.

The rocks in this arid basin leave trails of movement behind them.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.