Originally Posted by
Rob_E
Google shows a number of trails, but not necessarily linked up in a helpful manner. For the OP, Swain's Lock looks promising since it's on the trail and not too far from the city. If I understand the rules properly, you can't technically use it as a base camp and return for a second night, but it seems unlikely that anyone would keep track, especially if you struck camp and took your gear with you for the day. For my part, it will probably depend on how energetic I am at the end of my train ride. Swain's Lock is twice as far as Greenbelt, which also means twice as far on the ride back the next day. Might be worth it if I have the energy, just to put my wheels on the fabled C&O for a little while. But I might just want the closest place to hang my hammock and sleep.
Swain's is not twice as far, but certainly farther. Greenbelt Park is essentially at the Beltway, and Swain's Lock is 7 miles outside the Beltway, so you are looking at approximately 14 miles RT extra. However, the ride is scenic, mostly offroad and flat vs. urban, bad roads and hilly, and camping is free vs. a fee. No facilities other than water and portable toilets at Swain's, but you can freshen up at Great Falls.
As far as using it as a base camp, there is no one there to monitor its use. No one would know if you pack up and return the next night. Maybe if you set up for a week, the NPS would tell you to move on. I know of some who stealth camp in the woods along the towpath, but I wouldn't recommend.