What’s missing at Kassel, Germany is the opportunity to climb somewhere up on a tower to have good views on the city center. That’s probably also because most parts of the city center have been destroyed in World War II. You can only get to the Herkules monument to have a great view on the city.
A simply alternative is to use the multi-storey car park of the shopping mall Galeria Kaufhof for this. You can get up to the parking level P6 and then you can look down on the Friedrichsplatz, Fridericianum and the Königsstraße. During documenta times they sometimes open a rooftop bar there so that you can enjoy a drink while looking onto the city.
Parking level P6
Obere Königsstraße 31