https://gaptrail.org/

I did the DC to Pittsburgh--C&O Canal/GAP tour in 2023. On the whole, I enjoyed it though this was early July so hot and humid, plus the C&O was really muddy, which was tiresome after a while (had to stop twice to scrape mud out of my fenders to keep my wheels moving). That year the Paw Paw Tunnel was closed, and the hike-a-bike alternative was a real drag. I'd consider doing the ride in the opposite direction for the sake of variety.