The former Cologne art dealer has given, lent, and sold parts of his collection to Weimar, in eastern Germany

Will public art by Koons, Rauschenberg, Tinguely and Haring humanise this vast complex by Renzo Piano?

“We have wanted to create more of an essay than a history, so we made a list of artists who have done something decisive... or who created work that one simply cannot overlook”