Why not the more countryside areas of England? I really love walking around the Lake District in winter (less people), and there are not as many historical buildings (there are plenty of old buildings in the village which are just... old buildings and not of particular interest if you just want to have a drink at the pub) as there are very awesome walks. I walked for a couple of hours from Ambleside to Grasmere without really meeting anyone during one of my walks, and it was one of the more popular route.
Still, there are interesting things to look at, like Beatrix Potter's home and/or museum because they are so childlike and fun. I took a ferry to different parts of the Lake, walked for a couple of hours to Beatrix Potter's home (even though I knew it was closed) and saw nothing but sheep and sheep (had an encounter with one which was just staring at me), and had a really great lunch at the only pub in that tiny little village. I was incredibly relaxed the entire time I was there, and everyone was friendly which added to the experience.
I do know that it can get incredibly busy when the weather is better, so maybe September is one of those months?
And if you're done with Lake District, there are other fantastic areas in England itself that offers walks. Plus it's always only a train-ride to a bigger city if you miss the bustle.