Second Derbyshire/midlands, very nice natural areas
I also LOVEEEE Dartmoor, and Cornwall both. There are excellent places for searching for ammonites as well that I found many at. There is relatively easy access by bus to many spots, and one lovily thing about the UK is how very open access things are, you won’t get shot on all the public paths like you would wandering in the countryside in the US :) Pre-covid I used to go to the UK almost every year. I have some Dartmoor photos up on flickr https://www.flickr.com/photos/sunguramy/albums/72157677199168195
Tamar Valley is gorgeous. Careful at old mine sites don’t assume water is good (arsenic and other heavy metals from old mining operations)
Make sure to get a Prima Pasty if your go to the SW! :D