Famous castle in Winterthur

This is the view of Castle Kyburg (Schloss Kyburg) that I see every morning on my long 15 km Nordic trekking through the forests in Winterthur:

It’s over 1000 years old. You can’t really see WHY anyone would want a castle here, from this perspective, but in fact the castle sits above a river, and therefore it has a very strategic location – at least from a middle ages point-of-view.