Well, I am a great fan of the Sauerland and there are some really beautiful corners there. Like the Niederrhein it is devoid of tourists, although the outdoor activity possibilities are wonderful. Some of the towns are gems that somehow avoided the war. My friend had a holiday home at Holzhausen near Battenberg and Allendorf until deciding to sell it. Here are 2 links to hikes that I did in the Sauerland, although they were listed in the Ruhrgebiet book.

https://www.flyertalk.com/forum/34789736-post46.html

https://www.flyertalk.com/forum/34804321-post49.html