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

The final residence of an educator, civil rights leader, and presidential advisor was also the first headquarters of the National Council of Negro Women.

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.

A clone of a cloned tree that was so important it allegedly had its own guards.

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

There's a crumbling old mansion inside the Smithsonian National Zoo.

A nostalgic bibliographic gem.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

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

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

A painfully obvious spy house sits right across the street from the Russian Embassy.

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

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

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

The world's longest known cave system.

One of the Cemestos prefab homes built to secretly house thousands of Manhattan Project workers.

This hotel was used during the Manhattan Project to house official visitors.

John Hendrix predicted the creation of the "Secret City" built as part of the Manhattan Project.

Knoxville’s architectural icon was the symbol of the 1982 World’s Fair, even catching the googly eye of Bart Simpson.

This simple, broken column marks the final resting place of one of America's most famous explorers.

In 1912, a broken section of the reservoir wall released millions of gallons of water and destroyed many homes downhill.

This replica of the Greek structure is in the heart of Nashville.