I had some joy there in last autumn. Is here anyone interested? We can go there in some not-raining Sunday.
What you need is a bit courage and 20Euro ( less in group-price); What you will be returned is much fun!
Update on 17th Oct:
I have booked a group event there, and they offer us: 1, discount to around 17Euro; 2 English introduction; 3, A big group like 20 people.
If by bus, please take bus609 in HBF, Bonn, on Platform D2, 13:38, Sun. You should leave the bus at Nordwache, 13:55. Then go ahead for 100m, cross a bridge and turn right. You can easily see a landmark for HardtbergBad. That is our destination.
update on 23rd Oct
We have to change the date to Sat 14:00, because it will be rainy in Sunday afternoon. I will email you as well.