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

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

Drift through underground caves on a tube.

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

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

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

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

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.

Everyone from Alan Ginsberg to The Rolling Stones has stopped by this classic dive bar.

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

A steam trawler with a whiskey-soaked history driven ashore in 1960 resides rusty but still standing on the shoreline.

An outstanding and haunting glimpse of the horrors of the Great Famine of Ireland.

The ruins of a medieval monastery named after a type of tree.

After being destroyed by IRA sympathizers, the ruins of this stately Irish manor have sat vacant for decades.

A spectacular hidden beach in Ireland has the dark, disturbing nickname of "Murder Hole Beach."

The ancient tomb acts as a calendar that keeps perfect time.

This permanent collection of preserved bodies taken from Irish bogs is one of the leading authorities on such morbid mummies.

This floating garden in the sky is straight out of a fairy tale, but the real thing is nothing short of magical.

An Irish church where an 800-year-old mummy is reaching out of his coffin as if to shake hands.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

An Iron Age fort on the edge of a seaside cliff offers a glimpse into an ancient, mystical world.

An abandoned Art Deco hotel nestled on the side of a wooded mountain.

The world’s highest ski resort was deserted after an 18,000-year-old glacier melted away.