Getting to Sopot from Gdansk

I was there in 2015 to see some family history (my mother was born in current day Gdansk - then it was the Free City of Danzig)
We visited sopot by a private driver/van. We spent half a day and walked around the main part of town near the pier - the architecture is stunning and there was an outdoor fair selling all sorts of items and food (not sure what day it was).
On the way we stopped to see the cathedral Oliwska and attended a short organ concert - beautiful and highly recommend if you have time.

Take the local train.