Radboud Castle is a castle on the east bank of the harbour in Medemblik.
Radboud Castle is one of a number of castles in North Holland. The building was commissioned by Floris V, Count of Holland. When exactly it was built is unknown, but the castle was completed before the St. Lucia's Flood of 13 December 1287.
On 24 June 1517 the castle saved some of the Medemblik townsfolk from the raids of Grutte Pier and his Arumer Zwarte Hoop.
On 12 August 1588 the castle surrendered to Diederik Sonoy and the Geuzen.
The defensive function of the castle was reduced with the building of walls around the city of Medemblik in 1572 and due to both dismantling and lack of maintenance there was attrition of the castle buildings.