Home to items never before seen by the public.

The oldest continuously operating fish market in the United States.

Look closely and you’ll notice that the color changes a third of the way up the tower.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

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

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

The U.S. Fish Commission’s effort to mass produce carp.

On the Fourth of July this area will transform into a Pompeii-like storm of falling embers and ash.

The only tennis court that falls under the jurisdiction of the central bank.

The hippo that stands on this university campus was once a drunken flea market purchase.

Garments from across the globe call this hidden gem home.

There’s a hidden military meme engraved on the World War II Memorial.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

An echo chamber with a waterfall wrapped around its base at the Embassy of Canada in Washington, D.C.

A spectacular tribute to statesman and philanthropist Andrew Mellon.

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

A much-maligned monument to teetotalism.

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

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

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

A replica of the famous memorial statue at the Normandy American Cemetery hides in an office building in downtown D.C.

Once home to the largest photo service in the United States.

This nine-story building is the oldest standing skyscraper in D.C.