A small cave with a larger-than-life legend.

This unassuming home played a pivotal role in American history, essentially putting an end to the Revolutionary War.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

Disks are rolled out onto the south lawn to absorb the impact of Marine One's wheels like giant coffee coasters.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

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

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

Ruins from the Parthenon and petrified wood line the interior of one of the world's most famous monuments.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

After James Madison's death, his wife and former First Lady Dolley Madison lived in this yellow building near the White House.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

D.C. once had its own tiny rival to the New York Stock Exchange.

One of the three perfect vellum copies of this historic book known to exist is on display in a specially-designed case.

The Pentagon sits on a former island that was in Virginia at low tide and D.C. at high tide.

The Pentagon is so large that it was planned like a city, complete with internal highway infrastructure.

A former chicken restaurant that doubled as a speakeasy is now a quirky home full of wonderfully strange traditions.

An acoustic anomaly with a mysterious cause sits in the heart of Tulsa.

A half-size replica of the World Trade Center towers above Tulsa.

Once in disrepair, the house where the 1983 film was shot has been restored and turned into a museum.

One of the best examples of Art Deco architecture in the United States.

This 1930s-era Route 66 Tulsa landmark was moved, restored, and filled with neon.

Standing at 21-feet tall, this space cowboy adds to the legacy of Route 66's muffler men.

The fifth tallest statue in the United States is a shirtless monument to the oil worker.