Oppenau is situated in the Rench valley in the Black Forest. The nearest major cities are Offenburg and Freudenstadt.
https://en.wikipedia.org/wiki/Oppenau

At the Kreuz Inn, near Oppenau, the road to Freudenstadt and Antogast (see below) diverges to the r. At (6 M.) the busy little town of Oppenau (*Stahlbad; Post) “Kirschwasser' is largely manufactured.
Bædeker - Rhine, 1873