Château de l'Isle-Marie, Medieval fortress in Picauville, France.

Château de l'Isle-Marie is a late 17th-century residence in Picauville, built on the site of the old fortress of Holm. Its pale grey-brown stone facade has a central block with a steep dark grey roof and dormer windows, flanked by two projecting towers with conical roofs and two end pavilions. A red arched door is reached by a stone stair, and the building stands at the edge of a grassy field.

The first fortification at this site was documented in 1026 under the name Holmur, serving as a strategic point along an ancient medieval route. The structure was later expanded in the 17th century with new construction that gave it its present shape.

The name refers to its island setting between two rivers, reflecting the importance of water in the location's choice. Visitors can still sense the strong connection between the building and the surrounding waterways.

The château stands at the edge of the Beuzeville marshes, three kilometres south-east of the Saint-Candide church in Picauville, at the confluence of the Ouve and Merderet. The building is partly listed as a monument historique, so the exterior is what can be seen; the grounds are private and the interior is not open to visitors.

The castle stands on the site of the Holm fortress, whose name comes from the Old Norse holmr, "island", because winter floods of the Beuzeville marshes cut it off by water. In 1366, during the Hundred Years' War, attackers crossed its moats on large hurdles woven from reeds and rushes by local people.