How to get into the castle with a drawbridge?

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.