An acoustic anomaly with a mysterious cause.

This small piece of Michigan is entirely surrounded by Ohio.

A tunnel that brings more than a century of history to life from the deepest parts of the Niagara Gorge.

The blinking light atop the iconic landmark has been sending secret messages for decades.

Small plaque marks the spot, but the true center is located about half a mile away on a private pig farm.

See where Bill Murray kidnapped a hapless Punxsutawney Phil.

The final resting place of the world's first nuclear reactor.

The meeting of the northwestern corner of Delaware, the northeastern corner of Maryland, and the southern edge of Pennsylvania.

America's only nuclear missile silo open to the public.

Stepping away from the glitz of mobsters and casinos to learn about the other history of Vegas.

A luxurious doomsday bunker hidden beneath an unassuming Las Vegas home offers the best of subterranean suburbia.

At the largest railway museum in the United States, you can see everything from an early steam engine to a functioning Thomas the Tank Engine.

The "Seinfeld" diner.

A commemorative plaque hides a door that leads down to the New York Public Library's underground book bunker.

The home of aviation trailblazers, in a remote corner of the big city.

The sweet story of how American cargo planes became known as "Candy Bombers" during the Berlin Blockade.

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

The last SR-71 ever constructed.

The first integrated firehouse in Atlanta houses a museum on the history of desegregation in the city's fire department.

The first American department store, and home to the largest operating musical instrument in the world.

Where you can hail your favorite fictional commanders-in-chief.

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

A monument to the center of the North American continent may be off by a few miles.

These former Cold War launch sites have been preserved for tourists to see where the button might have been pushed.