There are 2 gyms in A'dam, both good, Het Lab is the biggest.
There's a gym in Haarlem just round the corner and there's 2 gyms in Utrecht, Sterk and Energiehaven).
Energiehaven (next to a train station) in Utrecht is the best gym in the Netherlands. 30 mins form A'dam by train.
Bussum (Rock Steady) ain't that far from A'dam and has some outdoor bouldering.