The Gdynia City Museum tells the story of how a fishing village of 1,300 became Poland's main Baltic port and a city of 250,000 in twenty years. The permanent exhibition runs from the medieval origins through the burst of 1920s and 30s construction, the destruction of 1939, the post-war population transfer (almost the entire pre-war population was German or had fled), and the post-Solidarity rebuilding.
The building itself is a clean modernist block from 2007 that pays homage to the 1930s. Allow two hours. The associated Bankowiec apartment museum (a preserved 1930s flat on Świętojańska) is on the same ticket — book a slot there in advance.