Something I like to do is look through Google Earth just to see what I can find. I came upon Lake Ladoga while looking for the origin of a certain type of traditional music. My question is a about an island on the western edge of the lake. The island, not named on Google Earth, has a large square structure on its far western point. It looks like a fort, with a large courtyard in the center.

Can anyone tell me what this structure is? Just curious.