The A6 from Derby to Matlock is the place to go when you want to see the Derwent Valley and its mills. It's a small road that crosses green valleys and passes tiny towns.
I started my tour in Belper, a somewhat larger town with a prominent mill (unfortunately closed today). The first mill I could get into was Cromford Mill. There are now shops and a small exhibition room, there's not much to see otherwise.
Finally, I went to Masson Mills. This is also turned into a shopping center, where you can buy fancy things like golf clubs and towels&soap. But there is more: a large part of the building is now a working textile museum. Here you can see the spinning and experience the noise in the large factory hall.