Brother Dennis and his friends Michelle and Klaus-Dieter when we were living on the economy in 1959. In January 2022 I received mail from Jan Nikolaus Viebrock, who was living in Frankfurt in 1959; he pointed out that this was an Edwardian motor rally in Frankfurt's Römerplatz (city hall square), organized by the Allgemeine Schnauferl-Club of Germany.  Jan contacted Frankfurt's Institut für Stadtgeschichte to get the details; the full response is here. Briefly, the Römerplatz was the gathering place and starting point for the rally, which started on 16 May 1959, which is therefore the date of this photo (and many of the other photos in this gallery, notably the next one).

Edwardian:

Referring to the reign of Edward VII of Britain and Ireland (etc), 1901-1910.

Schnauferl:

Vintage automobile.

Institut für Stadtgeschichte

Frankfurt Institute of City History and city archive