I stayed in the Castle Den for a few days this February with my dog, and it was nice...except that my dog kept hearing people walking around and occasionally talking upstairs, and it drove the dog nuts. This caused a bit of stress.
I don't know if the people upstairs were particularly noisy, or if the floor/ceiling is poorly insulated, but it was pretty obvious that we weren't alone. It wasn't loud enough to really bother me, but with a dog that wanted to bark at every noise...it was a problem. I didn't know it would be such a problem, so next time I'll be sure to rent a place where we are renting the entire building. I hope the occasional barks didn't bother the neighbors.
As to the flat itself: It's cute and comfortable, but...a bit awkward? I wanted nothing more but to relax on a couch or comfy chair while gazing at the view and/or fireplace, but the couch was placed with its back against the only window, so there wasn't an easy way to just kick back and contemplate nature. And the dining table was between the house and the fireplace, so you couldn't watch the fire either.
The bedroom I stayed in was very comfortable, though, and if you're planning to go off skiing during the day instead of sitting around inside like I did, it would be fine. And the yard was great for exploring with my dog.