Now a living classroom, this house was once the home of Reverend James Clinton Dent, a formerly enslaved man and a pastor.

Surrounded by a verdant garden and a backdrop of ivy, a monument to beloved poet Khalil Gibran stands outside of the Lebanese embassy.

A striking memorial to the 21 lives lost in an explosion at the Washington Arsenal

One of the first Second Empire-style buildings constructed in North America.

The final residence of an educator, civil rights leader, and presidential advisor was also the first headquarters of the National Council of Negro Women.

Garments from across the globe call this hidden gem home.

This apartment building designed by a notable Washington D.C. architect housed the Qing Dynasty's Legation.

The first museum in the U.S. to address human rights issues in China.

This groundbreaking 16th-century map is known as "America's birth certificate."

The former home of the woman who successfully fought to integrate restaurants in Washington, D.C.

Coins and medals straight from the mint await visitors to this shop in the nation's capital.

Depending on who you ask, this controversial treehouse is either a charmingly creative child's playhouse or an illegal encroachment on public land.

The only tennis court that falls under the jurisdiction of the central bank.

An amazing example of early-20th-century architecture, this church features marble transported from Utah.

Mysterious installations bring levity and light to a sometimes stodgy city.

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

The oldest house in Washington, D.C. wasn't originally constructed in the nation's capital.

This fertility idol of questionable authenticity inspired an iconic Indiana Jones artifact.

An obscure federal monument honors the French diplomat who served as Ambassador to the U.S. during WWI.

An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

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

These abandoned waterworks are crumbling into the Potomac River.

Amid the sprawling Defense Intelligence Agency Headquarters is one of Washington's least accessible museums.

A historic ruin just 20 feet away from a busy highway onramp.