I highly recommend this hotel if you're visiting the Black Forest. Gengenbach is a gorgeous little town, and this inn is right at the heart of it.
For the very reasonable sum of 38 euros I had a room with two beds, a separate shower room and separate toilet, plus breakfast. As always in Germany, the room was immaculate and the breakfast hearty. The Hotel-Restaurant Sonne is a traditional inn, family-run: mother, daughter and aunt serve in the restaurant, and son-in-law does the cooking. The fare is south-west German, so expect Kaesespaetzle (pasta with a cheese crust), Schnitzel, and satisfying meat-and-dumpling dishes. The food is delicious and the portions are generous.
I tried to pre-book via their web page, but a software bug made this impossible. After a frustrating half hour, I gave up and sent them an email instead. I received verbal confirmation of the booking on my voicemail - this was a nice touch. The owners really must sort out the web page problem - it could be losing business for them.
My only negative comment is that the family could have been more welcoming; they were rather unsmiling and reserved. Also, one of the clan tends to occupy the front doorstep for much of the day, chain-smoking cigarettes. This is not a good advert for the hotel, and makes you feel a little uncomfortable when using the front door.
I recommend going on the tour with the night watchman, who dresses in seventeenth century costume and stops at various landmarks to sing that "all's well". The tour costs nothing, and you get a real feel of what it would have been like to live in Gengenbach 300 years ago, when the watchman's songs would reassure the townsfolk that they could look forward to 'eine gute Nacht'.
I would definitely stay at this hotel again.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.