Giessen Old Castle, Medieval castle in Giessen, Germany.

Giessen Old Castle, also called the Landgräfliche Burg, stands in central Giessen between the Botanical Garden, the Kanzleiberg and the Brandplatz. Built around 1350 as a second moated castle extending the town defences, it was arranged around a narrow courtyard with a palas, a residential and a stable building, a linking wing and a tower with defensive wall and water-filled moat. The Heidenturm with its bulbous Welsche Haube and the main gate in the southeast survive from that layout.

The castle was built around 1350 as an extension of the town fortifications and as Gießen's second water castle. It is first documented in 1364 as a secondary seat of Landgrave Heinrich II of Hesse. Until the 19th century it served as a widow's residence, dwelling, secondary landgrave residence and court of law; from 1604 it housed a princely chancellery, which gave the neighbouring Kanzleiberg its name.

The name Kanzleiberg on the neighbouring street recalls the Fürstliche Kanzlei housed in the castle from 1604. The ground-floor Netanyasaal is named after Giessen's Israeli twin city and can be rented for events. The castle also holds a Gaststätte, and the Oberhessisches Museum's Gail collections fill its rooms.

The site sits in the city center and can be easily reached and explored on foot. An information board on site helps make sense of the medieval layout, which is worth reading before you start looking around.

The Heidenturm and the main gate in the southeast survived the 1903 neo-Renaissance rebuilding unchanged, and the tower still carries its Welsche Haube, a bulbous domed roof. The castle burned out completely in the 1944 air raids on Giessen; demolition plans were blocked and it was rebuilt in the late 1970s. Its ground-floor Netanyasaal is named after Giessen's Israeli twin city and can be rented for events.