This 15th-century island fortress later served as home to the executioners no one wanted to live near.

The secular incarnation of a religious meditation.

This legendary city has been a tourist attraction for centuries.

A quirky bookstore hidden beneath a sea of whitewashed Greek villas.

The spot in the Mile-High City that's exactly 5,280 feet above sea level (at least for now).

Inside the unassuming cemetery chapel is a magnificent stained glass window and mosaics.

This spectacular public market has got meat, fish, vegetables, baked goods, and enough kielbasa for a lifetime.

This steamer is known as "The ship that built Cleveland."

The only depiction of Abraham Lincoln holding a weapon, and the names of all 9,000 Cuyahoga veterans of the Civil War.

Funded by John D. Rockefeller, this is one of the earliest, and most beautiful, shopping arcades in America.

Ant sculptures march up the side of what used to be an iconic spot in punk rock lore.

The last of Philadelphia's wood-paved streets is now a landmark of terrible engineering.

This charming colonial alleyway is one of the oldest continuously used residential streets in the U.S.

Mrs. Mallard and her brood are a beloved fixture in Boston Public Garden.

An abandoned asylum incorporated into a college campus.

The only remnant of a small mining town is an abandoned railroad tunnel that is steeped in ghostly lore.

It took more than 20 years and a sharp eye for one man to assemble this quirky collection.

A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.

This Philly cemetery is the eternal home of many famous area residents, including Rocky Balboa's wife.

Ghost stories surrounded this “castle,” the only structure from a huge mansion that was never built.

This statue inspired by Renoir's famous painting embodies the jovial spirit of Key West.

Florida's oldest bar was once a morgue, complete with a hanging tree and gravestones.

The birthplace of American international flight service has been turned into a celebrity's microbrewery.

A monument celebrating the idea of reaching inaccessible places.