Thank you for your replies, all of you. Sex in public places is hot enough, but comes it with troubles and I do not want to use unsuspecting bystanders as a means to achieve or kinky goals. Seems like asking for trouble.
I'd rather like to know if there are places and clubs, much like swing clubs, where you can have sex - yes others may watch but no touching or swinging. I get it, the niche is specific but I'd bet it is not very uncommon.
And to the reply above, yes, we are planning to do it. We just do not know where and when will we work up the courage.
We travel quite a bit, that's why I am vague with the location. But Amsterdam sounds compelling