An artificial crater field that trained astronauts for lunar exploration.

This former railroad bridge was named after the great river that once flowed below it.

This community-driven organization uses education and eco-friendly technology to protect the environment.

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

The ruins of the first Spanish settlement in Puerto Rico.

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

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

An enchanting natural wonder in Puerto Rico's Camuy River Park.

This tiny home was originally a narrow alleyway.

Years of neglect and nature took a toll on this 19th-century lighthouse.

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

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

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.

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

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

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

The world's brightest bioluminescent bay.

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

Largest man-made excavation on earth!

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

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.