I was wandering around, trying to find all the question marks, when I decided to climb a mountain outside of Kaer Trolde (done from the opposite side, near the monster lair with the ghosts inside.) When I got to the top of the highest peak, I noticed a strange visual. In the of the main island of Skellige, there seems to be a bridge that runs into the opposite shore. It runs just to the West of the island inside up to the same area as the Crossroads Quick Travel.

When I died trying to get down, and quick traveled to the area, there was nothing. Nothing in the water seemed to suggest the water there was shallow or that there ever was supposed to be a bridge there. I'm curious to see if anybody knows anything that I don't.

P.S. Sorry for the bad quality, I'm playing on PC, and for some reason there doesn't seem to be a way to screen cap.

It may be the bad quality, but that doesn't look like a bridge to me, it looks like a vertical structure (some kind of tower?) I am going on the perspective: if it was a bridge, the far end would be much thinner, but seen in that image the edges look virtually parallel. That simply wouldn't happen at that distance.