The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

"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.

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

Railroad officials in the early 1900s sought to spare travelers the sight of Roman soldiers’ private parts.

Every autumn, this grove of living fossils erupts in a blaze of brilliant golden-yellow leaves and stinky fruit.

An eponymous directional signpost erected by the first president of the United States.

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

Experience the pivotal Civil War battle at this interactive museum.

Once a thriving business district, this former shopping area is now an urban ghost town in the heart of the city.

An abandoned church gets a second life as a massive beer hall and event space.

Public opinion is still divided on this enormous sculpture in front of Baltimore's Penn Station.

A faded sign from the 1920s remembers Baltimore's resistance toward banning alcohol.

The site of Neil Armstrong's first flight is marked by a full on replica of the moon landers.

A pair of 19th-century granite markers symbolically record where the state boundaries of New York, New Jersey, and Pennsylvania intersect.

Dim sum, served in a grand old theater.

This hidden labyrinth offers walkers some brief peace of mind.

Three prestigious academic collections come together to create a world-class natural history museum.

Impossibly life-like natural history models created out of glass by a father and son.

A perfectly crafted Pre-Columbian artifact dating back to 600 CE.

This impressive Boston holy house is the American mecca for Christian scientists.

Two thousand artifacts from around the world collected by one woman who loved to travel.

One of the now-less-hidden floral gems of the "Emerald Necklace."

A 17th-century Japanese bell brought back by U.S. sailors after WWII and later gifted as a symbol of peace.