Cologne is the largest city of Germany's most populous state of North Rhine-Westphalia and the fourth-most populous city in Germany. With 3.6 million people in the urban region and 1.1 million inhabitants within its city proper, Cologne is the largest city on the river Rhine and also the most populous city of both the Rhine-Ruhr Metropolitan Region and the Rhineland. Centered on the left bank of the Rhine, Cologne is about 35 kilometres southeast of NRW's state capital Düsseldorf and 25 kilometres northwest of Bonn. It is classified as a world city by GaWC.
The city's medieval Catholic Cologne Cathedral is a globally recognized landmark and one of the most visited sights and pilgrimage destinations in Europe. There are many institutions of higher education in the city, most notably the University of Cologne, one of Europe's oldest and largest universities; the Technical University of Cologne, Germany's largest university of applied sciences; and the German Sport University Cologne. It hosts three Max Planck science institutes and is a major research hub for the aerospace industry, with the German Aerospace Center and the European Astronaut Centre headquarters.