Prison de la Motte Castrale

The motte castrale is one of the town's founding sites and was used in the 10th century to protect the collegiate church from Norman invasions. Founded by the Counts of Flanders as the town's first castle, first with a wooden tower and then a stone keep, it later became the residence of the lord of Saint-Omer. Once again a defensive site from the 16th century, it was transformed into a military prison in the 18th century.

Today, the site hosts artists' residences. It is only open for festivals, special events and certain guided tours of the historic centre of Saint-Omer.