This Roman monument is surrounded by more recent construction, offering a stark contrast between ancient architecture and the modern urban landscape.

Home to what was once considered the largest gate in central Asia.

This miniature village stays behind in the Breuer Building, even as the museums around it come and go.

This lesser-known Frank Gehry building houses a treasure trove of cinema history.

Fake subway tiles were installed to cover a design that resembled the Confederate flag—it's unclear if the resemblance was intentional.

This picturesque monastery at the base of a cliff is a peaceful oasis open to all visitors.

Berkeley Hot Springs presents to you "the only outdoor monument to presidential bathing."

A sharply wedged sundial marks the point at which each day in the United States begins.

Rumored to be the famed pirate's lookout tower, this historic stone structure is now just watching for tourists.

This stucco building in North Africa was the first American-owned property on foreign soil.

If it hadn't been caught in time, a flaw in the design of this Manhattan skyscraper could have led to its collapse.

Backwards hour and minute hands and a timing mechanism that fluctuates with the temperature led to this clock tower's local nickname.

This outdoor gallery of sculptures along the East River was once a landfill.

An iconic Soviet statue of working-class people.

With over 10,000 lights, this engineering marvel lights up the city after dark.

Fresh wooden posts have been added to ancient holes to recreate a primitive henge clock.

Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

The Old Courthouse takes visitors on a captivating trip through St. Louis' timeline.

A creepy sculpture of a decapitated head invites viewers to see St. Louis through its empty eyes.

These red and black houses were awarded to the firefighters who saved their city from an enormous blaze.

The ruins of the first Spanish settlement in Puerto Rico.

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.

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