A geological mystery on Camelback Mountain.

The mysterious wonder of an underground waterfall is illuminated by multicolored lights.

After a water tower painting was accused of being an ad, a simple fix was made that gave the city a motto.

The oldest operating Mississippi River–style steamboat still navigates the Ohio River.

A 70,000-square-foot institution dedicated to a very literal, creationist perspective on the Book of Genesis.

A theme park featuring a replica of Noah's Ark built to the measurements specified in the Bible.

The world's tallest doric column is this Ohio monument to a naval victory in the War of 1812.

Take a drunken tour inside the world's largest known geode.

The final resting place of an unidentified revolutionary soldier sits behind a Virginia church.

The graveyard holding the remains of George Washington's slaves was forgotten for nearly 200 years.

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.

An overlooked memorial honoring the local Washington residents who died in World War I.

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.

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

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

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.

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

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

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

Decades before the scandal, this staircase on the river was a literal "water gate."

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

Perhaps the most scandalous statue of America's first president.