When I was 14 we went on holiday to Munich, as family friends had relocated there, and on a hot day we went to Englischer Garten, the huge park in the middle of the city. Which is also a nude sunbathing spot.
It was OK at first, but then some (slim, attractive) office worker woman came and laid down right next to us, after removing all her clothes. Then as it got busier we were surrounded by nakedness, including girls around my own age or a bit older. Mein gott.
I'd already had a few stirrings, but that day certainly turned the dial up a few notches. Probably broke the dial so it could never be turned down, actually.
Highlight was a German dude trying for quite some time to persuade his Canadian friend to remove her top. When she finally did it I felt like going up and high-fiving him, especially as she had fantastic, large breasts, the image of which is burned into my memory.
But standing up wouldn't have been a good idea. The Isar river there is fucking freezing, straight from an alp, so was useful for dampening down excitement.