Among others a giant, 100 meter high balloon (by the artist Christo) in the former Gasometer in Oberhausen. And a church by Scharoun. And a 1:1 scaled mockup of a Mies von der Rohe villa. And lots of modern architecture. And modern art museums with works of Anselm Kiefer and Gerhard Richter.
And good food, good beer and pleasant company.
This is a quickly sketched view towards some steelworks, as seen from the "tiger and the turtle magic mountain". That is a rollercoaster for pedestrians (no joke).