We recently trained at the
www.mejirogym.nl/ for four days training twice a day.
We stayed 2 minute walk away from the gym and which is 15 minute walk (if that) from Amsterdam Central.
Andre Mannaart takes most of the classes himself and they are 10 Euros a class for non members.
I would personally recommend the Mejiro.
Three of us went and are thinking about doing a longer trip there later in the year.
If you message the gym they are helpful with any questions.