This Kastellet is very nice to visit and it is great to find a cache her.
I had to try it twice in order to find it. First I came in the morning and when I was almost convinced that the cache isn't there any more I got caught be two military guys who told me to stay on the path. Nothing more happen and thy didn't see really interested in what I do here.
I cam back again in the evening and after a little bit more searching I found the little container at 19:38 o'clock! Very nice!
As the automatic translation I used to read this cache description is not very good I'm not sure if the task of finding the right canon is part of the game. There of I will not spoil on which one I found the cache. But in a other log I think I read that more than one canon should be searched...