So i stumbled uppon this castle that has some sort of treasure in it. I went all the way around and cant find a way to get in. Here are some screenshots detailing the location and look
It turns out there is a secret underwater entrance near the place of power. But you need to dive there for it to appear on the map
In addition to the underwater entrance near the place of power, I've found that a running leap can land you on the structure at the "hinge" of the drawbridge. To the right of the drawbridge among the bushes is a crumbled wall short enough for Geralt to do his legs-to-the side vault over.
I was able to 'climb' up the side of the rock where the castle is standing on and jump my way into the fortress. Didn't even know you could swim in until I was already inside.