On KNSM island, you'll find Fit aan 't IJ: a new club with an 'old school' look. With a view of the water, you can work out here in the Loods 6 building. The owner of Fit aan 't IJ is Jerry, who used to run the famous Jerry's Fitness. For strength training there is Matrix equipment and also for your cardio workout you can go here. The group workouts are also great. Especially the Hot Cycling on the new Keiser M3i (a 'magnetic spinning bike') is highly recommended. The TRX and the Fat Burning Step are also popular classes.
If you don't live nearby and come by car you can save yourself a lot of stress (and parking fees) by parking in the garage of the nearby shopping center 'Brazil', the first 1,5 hours are for free.
Make sure you arrive 15 minutes before the start of the lesson and bring a hand towel with you. There are lockers available free of charge. In the changing rooms, there are showers and a small infrared sauna. A towel is mandatory.
And get access to 396 gyms and studios in Amsterdam with one sports membership.