A super-sized promotional trick that is now a D.C. landmark.

The house where John Wilkes Booth conspired with his co-conspirators.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

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

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

Largest Roman Catholic church in North America.

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

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

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

The famous abolitionist’s preserved estate is one of Washington's finest monuments to its great Black citizens.

This leafy estate is worth $18 million and is so grand it has two mailing addresses.

The most decorated dog of World War I is preserved in the Smithsonian.

A rotating cast of guys and dolls in front of a Washington, D.C. building.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

The national park was once a plantation estate.

An Industrial Revolution-era public work that purified water using nothing but sand.

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

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

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

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

Fittingly, America's museum of architecture is itself a magnificently designed old building.

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

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