There are gay cruising areas in various places, and indeed one in the Vondelpark near the rosary. Most are 'informal' and condoned as long as there are no problems. There is large gay cruising area at the Oeverlanden near Nieuwe Meer (https://www.google.nl/maps/@52.3365124,4.8231607,17.5z?hl=en&authuser=0). There are signs that designate the area. People have sex openly there. Being straight it is not really for me.
We have two public naturist recreation areas, one in the Amsterdamse Bos (https://www.google.nl/maps/@52.3076171,4.8382419,17.75z?hl=en&authuser=0) and one near Gaasperplas (https://www.google.nl/maps/@52.3069271,4.9930967,19.25z). However, here sexual activity is not tolerated.
Unfortunately tolerance for nudity is decreasing, due to the influence of islamic immigrants.