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

A promising candidate for the lost rock laid by George Washington was unearthed, but the hunt is still on.

They sort through millions of dollars worth of diplomatic gifts on behalf of the government.

The first memorial dedicated solely to the Black troops who fought for the Union.

There's an old indoor swimming pool hidden directly underneath the White House Press Briefing Room.

This forgotten boat elevator was an engineering marvel in its heyday.

For 60 years, the academy had no permanent location until members voted Washington D.C. as its forever home.

The bugs crawling down the front of this office building are almost as big as a '68 VW Beetle.

An off-the-beaten-path place to literally hang beneath Milwaukee's Holton Street Bridge.

What appears to be a wizard's lair in Milwaukee actually houses a massive water pipe.

A group of artists transformed this desolate city alleyway into an outdoor gallery of street art.

This striking art museum holds an amazing series of curiosity cabinets.

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.

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

When it opened during the final years of the embargo, all the drinks and cigars were free.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

The New York hotel where tragic visionary Nikola Tesla spent his final hours, destitute and alone but for the pigeons.

This beloved marketplace mascot poops money and grants good luck.

The humble field where the first Major League Baseball game was played.

An Irish Memorial commemorating those who perished due to potato blight.

This elaborate towering structure was once famed for its revolutionary height.

This charming colonial alleyway is one of the oldest continuously used residential streets in the U.S.

A rare view of a preserved Victorian science museum.

This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.