That is the best city-festival I have been too ( 1996 , 2001) . But saddly it is only all few years.
Another huge festival in Germany is the annual the Hamburg ports-bithday or hbour birthday in May every year , stretching over 3 days with more than 1 million visitors the largest of this kind in the world , in Germanys largest port ( world # 8) and Germanys second city , with tons f things to do.