Talybont-on-Usk is worth looking at; there’s a YHA place at the foot of the reservoir dam, lots of riding and walking around the surrounding area, a canal runs through Talybont, so an inherently flat route that’s easy to follow. Talybont has two pubs, a B&B and a restaurant with rooms…
I’ve done some riding around there, years ago, and it was great fun. I keep meaning to get my bikes back out and rideable, and take my hooligan hardtail over and do some riding, I wouldn’t take the singlespeed though. A long-time friend of mine helps run the YHA there, so I’d have at least one person there to talk to and go for a drink with.