The Gdańsk branch of the Polish National Archives has two very interesting online exhibitions at the moment.
Gdynia miasto portowe: A series of photographs relating to the history and development of the city of Gdynia. Gdynia was founded in 1926 as a Polish rival to the Free City of Danzig.
90 lat diecezji gdańskiej: Photographs and documents concerning the Catholic church in the Danzig region over the past 90 years (including the Free City period).
Go have a look!