A labyrinth hides in plain sight at each of the city's 270 Tube stations.

It's a mystery why these remains were found with no traces of their bodies in sight.

One of Oxford's greatest treasures likely belonged to the legendary King Alfred the Great.

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

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

Washington's iconic carousel has a nice piece of Civil Rights history.

A rotating cast of guys and dolls in front of a Washington, D.C. building.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

This grand gothic brewery has been pumping out suds for over a hundred years.

Plot your trip through the city on the sidewalk.

A WWI fighter plane and turn-of-the-century penny candy shop are among the unexpected features of this Financial District building.

The "Seinfeld" diner.

The oldest operating apothecary in the US has treated everyone from Thomas Edison to Mark Twain.

This cemetery has graves dating back to the 17th century, including the city's oldest carved tombstone and an ominous cryptogram.

This unmarked and unloved Manhattan subway grate created one of the most iconic images in American cinema.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

A miniature rainforest is growing inside of a Midtown Manhattan office building.

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.