We are getting signals that Assumburg Castle is slowly being booked. So if you want to be sure of a stay in the Castle, you should book as early as possible!
One friendly advice: DO NOT book through intermediate sites like booking.com. You will not get a fair price. Instead, call the castle itself, on +31 251 232 288, and make sure to tell them you are booking for the great Beverwijk Judo tournament in April.
If you did not yet see the tournament outlines: They can be downloaded through this link.
The application form can be downloaded from the outlines, but also through this link.