The Dortmunder U is a former beer brewery and shows artworks from 20th and 21st centuries, develops innovative concepts of cultural education in the digital age, initiates partnerships between art and science, and cooperates with different players in the context of creative industries.
I was there a few times e.g. at the ‘moving types’ exhibition. It was really interesting. And at the top there is a observation deck where you can go for free and see the howl city!

for the program – check here
http://www.dortmunder-u.de/en/program

for more infos – check here
dortmunder-u_the-u

moving types:
http://www.moving-types.de/

for the NRW ticket – check here
Free trains in NRW