We're wrapping up with Civil War sites this week and did these two in the north part of DC a few days ago. Abraham Lincoln spent a lot of time at this house during the Civil War and Fort Stevens was the only fort in Washington DC where there was actual fighting during the war.
Fort Stevens isn't very big but it's partially restored unlike most of the forts in the area so it's worth a visit. There are a couple of interpretative signs there. In addition to being the only fort that had a battle at it in the District, it's also the only place where a sitting president of of the country has been fired at by enemy combatants.
The Lincoln Cottage is just a couple of miles from the fort on DoD land so there are lots of rules there. A few US presidents spent their summers there, when it was out in the boonies, but Abraham Lincoln is the one it's named after.
We weren't interested in paying $15 each for a tour and I almost didn't have us go here, but it looked like it was still worth visiting even without paying for a tour and it definitely was. You can walk around the outside of the cottage and read signs there, but there's also a visitor center that was really good with a lot of information about Lincoln. Don't skip this one because it looks expensive because it doesn't have to be to be worth it.
There's also a lovely display in the back of the VC about immigration.