An 18th-century Spanish watchtower made entirely of seashell and concrete.

The ruins of an open-air theater built on this Georgia island in the 1970s.

St. Augustine's record-setting narrow street was designed to protect against pirates.

Location of a reliquary containing bone fragments of 18 saints.

Only through the lens of a microscope can visitors see the true treasures inside this museum.

In this case, 'zero' marks the spot where the iconic Old Spanish Trail ends.

Intertwined, interspecies trees which locals believe can grant boons to lovers.

Despite being made of a seashell mortar, the crumbling remains of this historic Florida mill are still standing.

A luxurious 1880s hotel with its fair share of Tiffany stained glass, Edison electricity, and of course, ghosts.

The site of Martin Luther King Jr.'s arrest as he attempted to have lunch.

The first public building in Savannah to offer air conditioning was a luxurious cinema that still operates today.

A statue honoring 44 continuous years of greeting passing ships.

"X" marks the spot of an echo chamber in the middle of a plaza.

The walls of America's oldest masonry fort famously "swallowed" cannonballs.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

This kaleidoscopic mural shows Bob Dylan throughout his transition from young troubadour to Nobel laureate.

Jacksonville's highways rendered this century-old grammar school unusable.

The only arched bridge made of stone on the entire Mississippi River.

One of two giant blue cockerel statues erected with an intentional double meaning.

After the musical legend's death, his memorial was mysteriously graffitied in gold.

When flour explodes, it's not a pretty sight.

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

A display of magnificent stained glass windows is the first exhibit of its kind.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.