Dr Barnes' $25 billion private collection of art and arboretum.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

This grave marks the passing of a historic Jane Doe whose identity remains a mystery to this day.

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

The only home that Alexander Hamilton ever owned has a history almost as troubled as his own.

This area was once known for being a lawless haven for rough-and-tumble sailors, earning the maritime-themed nickname "the black sea."

This claimant to the title of "smallest church in the 48 states" doubles as an equally tiny, quasi-post office.

A sign at the end of the Santa Monica Pier marks the traditional end of the legendary American highway.

Michael Jackson got Bad and Crocodile Dundee walked on heads in this iconic Brooklyn subway station.

This Delaware River bridge is emblazoned with a catty slogan from a more prosperous time.

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

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

What was once a true peninsula has now been filled in, causing the water to recede and leaving many streetside "waterfronts" and landlocked "islands."

The remnants of two World's Fairs are here, complete with a 12-story globe, a mini-Manhattan, and a UFO-shaped pavilion.

Hear the quietest sound from across the dome.

The American Revolution was galvanized into serious action due to the tragic clash with British soldiers that occurred at this location.

Macabre headstones carved with winged skulls, dancing skeletons, and pithy reminders of impending death.

Elevated freight railway turned wildly successful urban park.

Haunting and beautiful trees, doomed to die.

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

Remains of a historic fountain that was mysteriously lost in the demolition of a D.C. traffic circle.