Ooidonk Castle, Renaissance château in Deinze, Belgium.

Ooidonk Castle is a red-brick water castle south of Bachte-Maria-Leerne, near Deinze, standing behind a lawn and a stretch of water. Its symmetrical facade is flanked by two round corner towers and centred on a taller square tower, all capped with dark onion-shaped roofs; two small pointed turrets sit beside the central tower. Rows of rectangular windows with light frames and a central entrance complete the front.

The site began in the 12th century as a fortified farm on a sand hill by a meander of the Leie, and by the 14th century it had grown into a water castle guarding Ghent. After the Battle of Nevele in 1381 it became the seat of the lordship of Nevele and passed to a branch of the French Montmorency family. Ghent troops destroyed it in 1491 and again in 1579; in 1592 Maarten della Faille bought the ruin and rebuilt it as a residence in Flemish Renaissance style.

The castle remains home to the Count t'Kint de Roodenbeke family, whose presence shapes how the rooms and grounds are cared for and presented. Walking through the interior reveals how nobility adapted their living spaces across centuries.

The castle interior has been open to visitors since 1958, from 1 April to 15 September; the surrounding French gardens can be visited all year. The domain sometimes hosts open-air exhibitions. The site lies south of Bachte-Maria-Leerne, near Deinze, in a 45-hectare park.

The castle's name comes from the sandy hill, a donk, beside a Leie meander where a fortified farm arose in the 12th century. For a time a beer called Kasteelbier Ooidonk, a label beer of Kasteelbier, was brewed under the castle's name. The surrounding Ooidonkbos, once a hunting ground, is now part of the Natura 2000 area Forests and Heaths of Sandy Flanders.