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

On a small Puerto Rican island, banks of secret naval bunkers lie abandoned and filled with piles of office equipment.

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.

Invading U.S. troops were first seen from this now-abandoned tower, leading to the Spanish-American War.

The crumbling remnants of this 19th-century quarantine hospital hint at the touristy island's darker past.

The location of Puerto Rico's first water bottling plant, thanks to a collaboration between Mother Nature and technology.

A fine, large-aperture telescope available for public use.

An extraordinary mixture of natural beauty and man-made phenomena.

A Nessie-like monster supposedly lurks in this lake.

This former fire tower is now a rustic observatory that offers amazing views of eagles, hawks, and the Appalachian Mountains.

Hidden behind Lincoln's head is a 70-foot-long chamber containing enamel plates documenting American history, sealed in a teakwood box in a titanium vault.

A futuristic climate change study is nestled deep within this public land.

This notorious Canadian mental institution was home to some of the first LSD experiments and origin of the word "psychedelic."

The crumbling structure is a rare surviving relic of the area's bygone mining industry.

Thanks to a loophole in property ownership, this alleyway has become a cacophonous street gallery.

14th century Norse artifacts in Northwestern Minnesota could have proved a Viking landing before Columbus.

One North Dakota man's vast collection of rare rocks, polished orbs, and geological wonders.

A museum, walk-through diorama, and library nestled under one castle-like roof.

Just a man taking his prehistoric pet for a stroll.

The deserted railroad town had a last gasp as a ghost town attraction before being abandoned for good.

This sprawling building built in 1890 was one of Minnesota’s earliest and largest mental health facilities.

A striking sculpture built to honor the women of the Lakota and Dakota Nations.

This sculpture gallery is home to magnificent beasts made of scrap metal and found objects.