I knew the gates would be ideal for a study of parallels. The castle was in the early days the summer residence of the French Ambassador to Switzerland. In the town of Solothurn, just down the road, you find the winter residence. Of course this was years ago, but it was a tradition.
I was looking for a link on the Internet about the castle but it is all in German. I once wrote a blog which might be helpful (plugging my stuff again).