Try these options for Oppenau:

Schwarzwaldhotel Erdrichshof
3-star
The Black Forest hotel „Erdrichshof“ is situated in Löcherberg among the magnificient landscape of the upper Rench valley, near the famous Bad Peterstal spa.

Höhenhotel Kalikutt
3-star
This family-run country hotel is situated at an altitude of 600 metres, in the Ramsbach district of Oppenau, in the Black Forest.

For more options see here: http://www.booking.com/city/de/oppenau.en.html

Good luck! -Guru