Best places to visit in Mannheim

Mannheim (German pronunciation: [ˈmanhaɪm]; Palatine German: Monnem or Mannem) is a city in the southwestern part of Germany, the third-largest in the German state of Baden-Württemberg after Stuttgart and Karlsruhe with a 2015 population of approximately 305,000 inhabitants.
It's 21:37 right now , with few clouds and the temperature of 18°C (64.4°F) in Mannheim.