G.S.B.V. de Mattekloppers is the student association for judo and jiu jitsu. You can join whether you are an absolute beginner or have been doing these sports your entire life.
Apart from the regular training sessions there are also lots of social activities, including having drinks, parties, and free martial arts workshops.
You can try out one of the trainings at any time, or you can sign up for one of the ACLO courses (judo, ju-jitsu, and self-defense).