Allowing humans and fish alike to migrate from freshwater to saltwater and back again.

This landmark cemetery in Boston was created more than 300 years ago.

"the sweltering inhabitants of Charleston and New Orleans, of Madras and Bombay and Calcutta, drink at my well . . . The pure Walden water is mingled with the sacred water of the Ganges."

A toweringly silly piece of modern art has been delighting locals since the 1980s.

A geological mystery on Camelback Mountain.

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

A museum dedicated to the alleged Roswell Incident.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

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

This massive tea kettle was once a promotional stunt for the Oriental Teashop.

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

A massive sea stack famous for its appearance in The Goonies.

A spiritual vortex among the red rocks in Sedona.

The 340-year-old house that inspired the classic Nathaniel Hawthorne novel.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

Scattered throughout London are ancient remnants of the city's former bounding wall.

An interesting decoration on this historic site, this weathervane comes with as many legends as it does questions.

A dramatic, 360-degree recreation of Pickett's Charge in the Civil War.

The site of Paul Revere's historic two lantern warning.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

The only structure left with direct ties to the Salem witchcraft trials of 1692.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

A fitting attraction for the corn capital of the world.

The world's longest known cave system.