The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

This Arizona observatory is famous for investigations into Martian life, and as the place humans first spotted Pluto.

One of America's first spies started out as a teacher in this little red one-room schoolhouse.

The ruins of an abandoned 18th-century town that is slowly being reclaimed by the forest.

The US Navy's only submarine museum is also home to the world's first nuclear submarine.

While many places make the claim, the Library of Congress says this restaurant is the birthplace of the hamburger.

A portrait of the Charter Oak hangs in a frame made from the Charter Oak.

An abandoned gun-funded 19th century utopia.

A wunderkammer hidden on the top floor of the Hartford statehouse.

The oldest place in Hartford is a cemetery with thousands of bodies stacked beneath the grass.

Northern Ireland's Brobdingnagian stepping stones.

Quirky castle designed by the American actor best known for portraying Sherlock Holmes on stage.

The decorations were inspired by an unlikely missing treasure.

This playground sculpture of an icon from the past is dedicated to the children of the future.

Local legend has it that an old, decaying staircase outside this cemetery is haunted by dozens of ghosts.

This inanimate goat created by the "welding nun" has been helping to clean up the city of Spokane for more than 40 years.

This historic national park is covered in the stunning ruins of red rock pueblos.

An enormous, inside-out glass globe built in 1935.

A wall of chewing gum moonlights as collective art.

A giant Troll lurks under one of Seattle's oldest bridges.

An outsider art duo's yard has been turned into a whimsical public gallery.

The former home of Samuel Clemens and family remembers the happiest period of the author's life.

A former copper mine which became a truly unsuccessful prison.

This lovely hilltop tower was specifically built to withstand 100 MPH winds.