Being no particular fan of industrial history, I just went to Essen to see another WH site, but I was pleasantly surprised. Zollverein is a really big (14 sq.km) industrial complex that was the biggest coal mine of its day (1920s and 30s), and the grand industrial architecture served the purpose of impressing visitors with the mine owner's wealth and power. I took a guided tour that took almost 2.5 hours - the guide was really great and very informative. Now I know everything I never thought I wanted to know about coal-mining and especially about the miserable and dangerous lives of the miners there. The site is interesting for its architectural as well as economic and social history, and definitely deserves a visit.