While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

An overlooked memorial honoring the local Washington residents who died in World War I.

Three abandoned missile silos are hiding in plain sight behind a suburban development in Maryland.

The world's oldest continuously operating airport was founded by the Wright Brothers.

The tallest The Church of Jesus Christ of Latter-day Saints temple in the world soars above the Beltway.

A daily replay of the experiment that proved the rotation of the Earth.

This historic old movie house was the scene of one of the Blob's most iconic attacks.

This dramatic rail curve was once the target of a failed Nazi attack.

A local prank turned town icon.

This elaborate towering structure was once famed for its revolutionary height.

The oldest farmer's market in America is so ancient it was approved by the King of England.

A failed piece of Orientalism has become the proud symbol of a community.

The house that Frank Lloyd Wright "(shook) out of his sleeve at will" at the age of 86.

In which a local geological marvel becomes a quaint roadside attraction.

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

A layered tribute to the work of mosaicist Isaiah Zagar.

A toxic ghost town sitting atop a massive coal fire.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

The only visible reminders of an elaborate engineering project that kept the tower from reaching the tipping point.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Da Vinci's equestrian statue, 500 years in the making.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

The vast, legendary catacombs hold secrets much stranger than stacked bones.