Boats leave hourly from the centre of Gdansk to sail up the river to the small peninsular at the rivers mouth into the Baltic
At Westerplatte you can get off and visit the War ruins, the location of the start of the Second World War and re-join a later boar, or you can stay on the boat and go back into Gdansk
It is also possible to get on way tickets, and then catch the bus back into town (or vice-versa)
The tour is accompanied by a commentary, but in Polish only