You don't have to finish, as far as I'm aware. Go downstairs, into the sewers, and you should reach a path that with two gates opposite each other. The diagram is in a chest behind the wall in between those gates, that I think you need to find a switch on the wall for.Get Junior
But I can not open that gate
I can see the breakable wall if I go through to the
Junior mansion basement entrance
And unrelated. Holy shit. The music/atmosphere in Skellige is god tier. Amazing stuff so far.