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

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

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

A street in front of NASA's D.C. headquarters has been named in honor of the Black women who were essential to early spaceflight.

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.