- Giessen is a city in central Germany, located in the state of Hesse. It is situated on the banks of the Lahn River and has a population of approximately 86,000 people. The city is known for its rich history, with settlements dating back to the Roman era. Giessen is home to the Justus Liebig University, which is one of Germany's oldest universities and a major research institution. The city also has a vibrant cultural scene, with theaters, museums, and various festivals throughout the year. Additionally, Giessen is known for its picturesque landscapes, including the nearby nature reserve of Klosterwald.