Diepenbeek Castle  Diepenbeek Castle (, also known as the "Rentmeesterij van Alden Biesen") is a castle in Diepenbeek near Hasselt in the province of Limburg, Belgium. The building consists of a 15th-century keep with a 17th-century main block. It was once the establishment of the steward () of the nearby Commandery of Alden Biesen, whence the alternative name.