One of the oldest living oak trees in the Southeast.

A waterfall 600 ft. inside a mountain, once the bane of gold miners, is now a spectacle of nature.

Known as "The Hill of the Little Devils."

This geodesic gallery holds a collection of painted spheres that make traditional canvases look lazy by comparison.

An entire city block built completely out of petrified wood.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

Hidden behind Lincoln's head is a 70-foot-long chamber containing enamel plates documenting American history, sealed in a teakwood box in a titanium vault.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

More than 500 unique and specially designed cases collected by D.C.'s "Harmonica Case Man."

Amid the sprawling Defense Intelligence Agency Headquarters is one of Washington's least accessible museums.

Before founding the American Red Cross, Clara Barton had a tremendous humanitarian impact by locating thousands of missing soldiers.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

This unique museum cafeteria showcases the history and regional diversity of African American cuisine.

Senators used to relax in the nearly forgotten marble tubs now hidden in the U.S. Capitol Building's basement.

The institution is sitting on a goldmine of 21,000 paints, varnishes, pigments, and primers preserved for posterity.

Perhaps the most scandalous statue of America's first president.

A museum cafe showcases Native American dishes and indigenous ingredients from across the Western Hemisphere.

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.

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

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

A derelict bit of transportation infrastructure hidden in the woods.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

Local legend says that someone is buried in the trunk.