Apparently he was getting up to all sort of antics not dissimilar to what you see real bears and other animals get up to in zoos.

According to Metro it was "...a performance where he dressed in a bear suit and spent ten nights alone...Outside this huge glass box of a building small crowds would gather to watch his lonely antics, which, like real bears in a zoo, were often more disturbing than entertaining".

I don't know what that last comment means but the only picture I can find is of him standing up in it so I can't work out what these antics would be.