This Old West prison built into the side of a cliff was said to be inescapable.

Since World War II people have been decorating this stretch of the Yuma desert with signatures arranged out of rocks.

This ancient trail has claimed the lives of over 2,000 people.

On this Puerto Rican island, many abandoned naval ammunition bunkers sit open while a few have been padlocked by locals as personal storage.

This small primate research island is teeming with playing, fighting wild monkeys.

This bleach-white graveyard overlooking the ocean is accessed through a tunnel.

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

This chapel on a cliff is renowned for its healing powers and was founded on the site of a supposed divine intervention.

This small fort played a huge role defending Puerto Rico’s capital city.

The bat-covered home of one of the world's most popular brands of rum is located on a tropical Art Deco campus.

This 20th-century mansion plays a key role in one of Puerto Rico's greatest novels.

This former sugarcane transport tunnel is now a portal to a lovely beach.

This giant bronze image of Christopher Columbus embarked on a voyage of its own.

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

This niche museum devoted to ancient religious artifacts is shaped like the very thing it displays.

The highest peak in Puerto Rico is home to a rare fern that can only be found on six trees at its summit.

This ''hidden'' 19th-century bridge played a simple, yet important role during the Spanish-American War.

This nearly abandoned "company town" is a ghost of Puerto Rico's once-lucrative sugar industry.

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

Outsider Art Community.

The largest natural travertine bridge in the world is nestled in a small canyon in central Arizona.

A partial tunnel blasted into a steep ridge is all that remains of a failed railway across Arizona.

The eerie ruins of an isolated abandoned town nicknamed "the Widowmaker" for its deadly gold mine.

At this deceptively beautiful beach, nothing is what it seems.