This cannon dating to 1755 has stood guard at this suburban intersection since 1915.

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

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

America's first federal monument.

The narrowest house in America is seven feet of pure spite.

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

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.

In a pedestrian tunnel on North Carolina State’s campus resides an expressive and artistic free-for-all.

A former Confederate hospital serves as a remembrance of wounded and dead soldiers.

This research center for rare prosimians is studying how they sleep to help prolong human life.

Elaborate tile work in this railway station tells the story of Portugal.

This giant sculpture made of trash is a critique of society's wastefulness.

This rare basilica nestled right in downtown Asheville is an architectural marvel, inside and out.

A giant concrete churn carries the legacy of American resilience, unity, and greed.

This bright yellow relic is the final survivor of a short burst of seashell-shaped petrol pumps.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

There’s a hidden military meme engraved on the World War II Memorial.

The largest hewn stone in history.

A patchwork of ruins from various civilizations in one of the world's oldest continually inhabited cities.

New York's oldest concrete structure is being preserved thanks to the gentrification of Whole Foods.

This cemetery served as the only official burial grounds in Cambridge for nearly 200 years.

Tiny artwork tucked within glass letterboxes form this hidden gem of an art gallery.

This now-deactivated naval base defended the Florida coast for centuries.

Less a museum than a bizarre fantasy world created by artists and engineers.