We're going to explore one of the true hidden wonders of Washington, D.C., a Civil War fort nestled deep in Rock Creek Park.

In July, 1864, a Confederate Army attempted a surprise invasion of Washington, D.C., hoping to sow panic and drive Congress and President Lincoln from the Capitol. Confederate forces swept into the city, and fought a desperate battle among the northern defenses of Washington. President Lincoln rode over to the see the fighting, the only time in American history a president has been under enemy fire. Eventually Union forces repelled the attack, and Washington was saved. It’s considered one of the greatest what-ifs in American history: Had the Union lost the battle, most historians believe there would have been a negotiated settlement to the war, and a durable Confederate nation.

We’re going to visit Fort DeRussy, one of the forts that drove back the Confederate attack, and learn the full story of how the Civil War came to Washington. Abandoned after the war and overgrown, Fort DeRussy was practically lost to history. Today, it’s virtually unknown: I grew up blocks away and didn't even know it was there. It's an astonishing, beautiful ruin in a peaceful forest grove.