Few cities have been at the center of European history as often as Gdańsk. For centuries it was Danzig, a rich, German-speaking Hanseatic port that lived off Polish grain. The Teutonic Knights seized it in 1308 and massacred many of its people. In 1454 the city rose against them, pulled down their castle and went over to the Polish king, who rewarded it with privileges so generous that from then on it answered to him only when it suited it. Between the wars it was a Free City under the League of Nations, and on 1 September 1939 the first shots of World War II were fired at its harbor. In 1980 a strike at its shipyard gave birth to Solidarity, the movement that brought down communism in Poland and then in half of Europe.
What you see today is mostly rebuilt. In March 1945 the Red Army took the city and set much of the old center on fire after the fighting was over, and about 90% of it was destroyed. The Germans were expelled, Poles arrived, many of them expelled themselves from Vilnius, Lviv and the lost eastern lands, and over the next decades they put the brick churches and gabled houses back up. That story is as interesting as the buildings, and it's one reason Gdańsk deserves more than the day most cruise passengers give it. The other is the Tricity: Gdańsk runs straight into the seaside resort of Sopot and the 1930s port of Gdynia, with beaches, a long wooden pier and the Baltic on the doorstep.
This plan keeps each day in one part of the city. Day one is the Main Town and the Royal Route, day two the war, from the WWII Museum to Westerplatte, day three the Old Town and the shipyard where Solidarity began, day four Oliwa, Sopot and Gdynia, and day five a trip to Malbork, the largest brick castle in the world. If you have longer, the Hel peninsula, Kashubia and the dunes come after day five. Most museums here close on Mondays or Tuesdays, and the plan fits them best if day one is a Wednesday.