The largest Neolithic ruins in the world hide a notably clean prehistoric metropolis.

A sacred lake with thousands of sacred carp and a biblical history.

This hunter-gatherer architecture is believed to be the oldest religious complex known.

Mausoleum and Holy Seat of Antiochus I of Commagene.

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

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

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

Washington's iconic carousel has a nice piece of Civil Rights history.

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

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

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

Home to items never before seen by the public.

The oldest continuously operating fish market in the United States.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

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.

Funded by John D. Rockefeller, this is one of the earliest, and most beautiful, shopping arcades in America.

The overgrown remains of an old rail bridge rise above the valley like ancient Greek ruins.

This whimsical park encourages its visitors and wildlife to roam on and around the various works of art.

A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

The lynching and burial site of America's first train robbers.

A lesser-known part of the Kinsey Institute is this impressive collection of art, artifacts, and material culture related to human sexuality.

One of the largest collections of merchandise from the famous British sci-fi show can be found smack in the middle of Indiana.

This mysterious hill seems to pull objects uphill.

The first spinning jail built in the United States is the only one that still turns.