Kaer Morhen (The Witcher 3: Wild Hunt)

How to get there? I just got to skellige, I didn’t go through anything there, in general I didn’t advance much in the plot, I’m still looking for the treasure of the Redanian spy, I collected a bunch of sets (17 ur current, I know I don’t need them, but still, I’m burning with the desire to get into the cloister of the witchers for the next, and indeed it pulls there). Is there a way to get there without going through any storylines? Thank you in advance.