This softly rounded mansion was built without corners not to avoid evil spirits, but to make them more comfortable.

Rare recess caves fill this unbelievably beautiful Ohio park.

An exhibit of items from the mental institution where Mary Todd Lincoln lived after her son conspired to have her committed.

Arguably the best example of an authentic Dutch windmill in the United States, rivaling its counterparts in the Netherlands.

A replica viking ship from the Chicago World's Fair is still in dry dock in an Illinois park.

This cemetery is all that remains of a school for "wayward" girls.

This house renovated by Frank Lloyd Wright was the centerpiece of a lavish 20th-century estate.

One man has spent decades faithfully constructing this unique brick and cinderblock castle.

A miscalculation turns a very shallow freshwater lake into a very deep saltwater lake.

Once the extravagant escape of the Ford family, this enigmatic ruin now stands as a haunting reminder of its former glory.

In Hong Kong, a fairytale flower tunnel is hidden within the gardens of a public housing complex.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

An abandoned railroad tunnel transformed into a creepy path for hikers and cyclists.

This massive, 30-foot-tall statue of the famed Scottish knight overlooks a grassy knoll.

The oldest house in Washington, D.C. wasn't originally constructed in the nation's capital.

The world's oldest soul food restaurant is also one of its best.

Coins and medals straight from the mint await visitors to this shop in the nation's capital.

A rare example of a rural school in Washington, D.C.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

These azure waters were thought to lead to the Mayan Underworld.

There's a mini version of Iguazu Falls hidden in the Balkans, and it's got a rope swing.

A long-forgotten Victorian swimming hole is still a fun spot for a dip.

Take a dip beneath the stalactites in this amazing cenote.