For decades, it has disappeared and reappeared as water levels rise and fall.

The only geyser in the state of Pennsylvania is caused by pressure from an abandoned coal mine outside of the ghost town Centralia.

Behold the rickety wooden glory of the world's oldest operating roller coaster.

The graffitied ruins stand hidden within the Pennsylvania woods.

This little museum in the town where zombies were born celebrates the living dead.

This eerily well-preserved coal town was saved from destruction by a Sean Connery movie.

These tourist trap caverns are said to be the former home of a legendary Pennsylvania Hermit.

Faces carved into the cliffs create an otherworldly walking trail.

This elaborately-carved white marble fountain was built to stand outside the Detroit Opera House.

Once a sewer culvert, this road tunnel now offers cyclists and pedestrians a subterranean stroll under the C&O Canal.

The word "Watergate" will forever be associated with the infamous scandal in 1972, but this fountain is famous in its own right.

Before Nixon, "watergate" meant canals.

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

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 haunting tribute to pioneering photographer Clover Adams.

The house where John Wilkes Booth conspired with his co-conspirators.

There's a crumbling old mansion inside the Smithsonian National Zoo.

The national park was once a plantation estate.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

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

A derelict bit of transportation infrastructure hidden in the woods.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

A painfully obvious spy house sits right across the street from the Russian Embassy.