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

It's a pretty creepy lock-up.

A centuries-old church stands as a testament to Boston's "father of architecture."

The modern birthplace of Irish freedom.

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

A hugely vast Irish landscape of barren rock that stretches for miles.

This modest plaza in Moneygall, Ireland has cashed in on its distant connection to the U.S. president.

One of corporate America's best-kept secrets is also one of the most publicly displayed.

Atlanta's strange assortment of concrete pillars inspires reflection in some, confusion in others.

An underground magnet for ever-changing street art.

It was once nicknamed "the most bombed hotel in Europe."

A statue honoring 44 continuous years of greeting passing ships.

This twisty sign depicts the chain's first logo.

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

An early-19th-century hotel with a past that is steeped in the Civil War.

A once-groundbreaking power plant turned into a hotel and mini-museum of archeological and geological wonders.

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

This quirky curiosity shop takes its cues from the world's bazaars.

Commemorating the landing of William of Orange with his European army on their way to the Battle of the Boyne.

This castle once belonged to one of the most prominent families of medieval Carrickfergus.

The ruins of this medieval castle in Northern Ireland have inspired artists from C.S. Lewis to Led Zeppelin.

Northern Ireland's Brobdingnagian stepping stones.

The atmospheric road was never meant to be so creepy.

This stone harbor was key to Carnlough's limestone industry.