Travel / Going to Kraków, Gdańsk, Słupsk, Szczecin... [10]

My Wife and I are going to travel by train from Gadansk to Krakow via Torun in June. We will have 2nights in Gdansk and Torun ,and 3 in Krakow. Any tips or suggestions ?

I'm new to this forum and not sure if this is in the right place !