After 950 km. drive. we arrived a little before 9pm and checked in with a very kind and helpful receptionist. Had seen on the homepage that the restaurent should be open to 10pm. We went to the restaurent at 9pm - at the same time when two meals were carried from the kitchen in to some guests. But: We were rejected a table (even there were many empty tables) by a quite negative and unfriendly waiter, because we had not made a reservation. If we had not made a reservation, we were told, we could not expect that the kitchen had procured enough raw materials for feeding us. Even we asked for what disches they had materials to cook - and offered to just order that, we were still refused.
We ended up walking through the city to maybe 5 restaurents with "closed klitchen" before we found one who served some very good ribs, at a small place called "Rib Publik", Shilderstrasse 57. But, this is simply not good enough at a relatively expensive hotel like Hotel Der Achtermann.