An artsy hidden staircase leads to breathtaking views of San Francisco.

A huge musical instrument played by the ocean.

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

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

The "lovely red Vega" of the legendary record-settling pilot.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

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

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

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

An amazing example of early-20th-century architecture, this church features marble transported from Utah.

The tunnel under the Capitol Building where Congress takes out its trash.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

The innocent intentions of this monument are somewhat lost in the sculpture's muscled imagery.

A line of blue paint marks the route of the inaugural parade.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

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!”

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

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

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.