I don't know if I am missing something or what, but this mark (map attached) still there and I can't do anything.
I went in different times of the day, but nothing happen. Maybe I have to do something before to activate it or go in an exact hour.

Someone else have this "problem"?

That's funny, it's in the middle of the lake. Did you dive there? Sadly I don't remember a quest in this location.

Thanks for reply.

You can't dive there, cause is like a... ¿puddle?, not deep enough to do it. I put some pictures of the place, maybe someone remember what happen there.

PD: I kill the nekkers appearing in the pics.

Interesting thing about this place is that its coordinates are: x=0 & y=0.
If you have a console activated type xy(0,0) while you are in Velen and you get there.
And don't forget type 'god' first, or repeat xy(0,0) again when you falling.
I don't remember any missions here and I played this game 4 times already.

I went to this location and there was no quest there in my game. It could be a bug.

The map is obviously wrong, because there is no lake there, like the map suggests. But besides that I couldn't find anything.

Well, I couldn't find anything. I continued playing and finished the game.

I'll see when I replay the game if there is something there or not.

Thanks you all for reply.