It is located in east part of the old town overlooking the canal. It is next to a pleasant eco restaurant and also very near to not so eco Aldi. It is 30 minutes walk from the train station, maybe best to get bus if you have big rucksack, get off in the main shopping street and walk 10 minutes to the Rucksack hotel. It is well appointed, with kitchen, dorm beds were solid, toilets worked OK. I can understand that there are booking problems, yes the owner does not answer the phone much. She is a little eccentric, now I understand what happened to the hippies from the 60s, they run gjesthouses and backpackers places.
I did not book ahead, I just turned up, and there was a young lady who worked there. There were plenty of beds even in July. I suppose many Germans were taking their holidays is sunnier climes.