All these clubs in the Frankfurt area are "fully nude" ,which these days means mostly nude, clubs. Lingerie day shown in brackets. My experience is that on lingerie day, some girls still go topless and, as the evening wears on and they are short of business, more and more of the girls wander around topless.
FKK World near Giessen: (Tuesday)
FKk Oase near Bad Homburg: (Thursday)
FKK Palace in Frankfurt: (Wednesday)
FKK Sharks in Darmstadt: (Tuesday)
I also believe that FKK Babylon in Elsdorf near Cologne is fully nude.
None of the NRW clubs are officially FKK but, in my experience, about 25% of the girls are topless, especially those with very good tits.