Mülheim, officially Mülheim an der Ruhr and also described as "City on the River", is a city in North Rhine-Westphalia in western Germany. It is l…Mülheim, officially Mülheim an der Ruhr and also described as "City on the River", is a city in North Rhine-Westphalia in western Germany. It is located in the Ruhr Area between Duisburg, Essen, Oberhausen and Ratingen. It is home to many companies, and two Max Planck Institutes.