Washington's top-secret Cold War-era doomsday communications tower is located in a small neighborhood park.

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

The school tested mustard gas for the U.S. Army during World War I.

These unusual rooms on wheels are holdovers from the 1960s.

Bubbling up from deep underground is the warm crystal clear water that fills the Warm Springs Pools, America's oldest spa.

America's post-nuclear-attack chambers of Congress.

One of the oldest standing structures in Montgomery County, Maryland.

The bridge's highly-contested plaque (once again) honors Confederate President Jefferson Davis.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

This campus chapel is Robert E. Lee's final resting place and a topic of debate about the legacy of the Civil War.

The final home of the most famous horse of the American Civil War.

The only recreation of William Shakespeare's indoor playhouse.

The only ski tunnel in North America provides easy access to amazing snow and beautiful views.

The mysterious canine hides atop a drain pipe on the back of the building, some say as a sneaky shoutout to Yale.

Nassau Hall has served as army barracks, a museum, and played a key role in the American Revolution.

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

An overlooked memorial honoring the local Washington residents who died in World War I.

A replica of the famous memorial statue at the Normandy American Cemetery hides in an office building in downtown D.C.

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

A centuries-old church stands as a testament to Boston's "father of architecture."