It is the largest city of Germany's most populous state of North Rhine-Westphalia (NRW) and the fourth-most populous city and one of the oldest in Germany. The city's medieval Catholic Cologne Cathedral (Kölner Dom) is the third-tallest church and tallest cathedral in the world.
Cologne is a very pretty city located by the Rhine river. It is known for its big cathedral, which really is amazing. I also recommend visiting the city centre and the Rhein promenade.