The ones from Migros offer classes as well as Holmes Place but they all have the same principles: once the class is full you cannot attend. So you have to be early for certain popular classes in order to secure a space.

More infos on Migros Fitnessparks can be found here http://www.fitnesspark.ch/ and for Holmes Place here http://www.holmesplace.ch/en-ch/club...ess.Zurich.php