An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

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

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

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.

This statue of the "father of television" stands prominently in the United States Capitol.

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

One of the three perfect vellum copies of this historic book known to exist is on display in a specially-designed case.

This groundbreaking 16th-century map is known as "America's birth certificate."

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

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

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.

Need a hardcopy of the 50-title Code of Federal Regulations? This is the place.

Atop this media building, two hives containing more than 30,000 bees keep the surrounding area vibrant.

An easily overlooked memorial to a Ukrainian famine-genocide that killed over 4 million people.

Railroad officials in the early 1900s sought to spare travelers the sight of Roman soldiers’ private parts.

A historic arena where the Beatles played their first concert in the U.S.

An unexpected alley with light shows and nature views.

In addition to over 80 vehicles on display covering over 100 years of motorcycle history, this free museum focuses on the people who ride and love these bikes.

Victorian "Fancy Craft" Hair Wreaths and Relics.

This Boeing KC-97 tanker is now a restaurant for aviation lovers.

"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 hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

After his presidency, George Washington planned to live only a few blocks from the Capitol building.

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