A former major munitions plant that has been converted into a sprawling art space.

This colonial tavern played host to George Washington, Thomas Jefferson, and other famous early Americans.

A massive, majestic mammal watches over pedestrians from his perch atop a former B.P.O.E. lodge.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.

This pharmacist and his patient greet visitors to the National Community Pharmacists Association.

Long buried under the 20th-century landscape, this lift lock of the Alexandria Canal is the lone remnant of an ambitious early American transportation project.

This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.

The world's brightest bioluminescent bay.

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

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

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

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.

Enjoy the waters of this half-moon-shaped natural pool surrounded by breathtaking scenery.

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

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

This colorful gate stands as an entrance to the walled city of Old San Juan.

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

On a clear day, you can see all the way to the Virgin Islands from the top of this observation tower built in the 1960s.

A magnificent waterfall nestled in the heart of the El Yunque National Forest.

Nine limestone rock stacks on Australia's "Shipwreck Coast."

This public art is inspired by a local Aboriginal creation story.

These flying foxes dangle from the trees around the library like fuzzy black fruit.