Jest to bardzo fajna sprawa. W Świnoujściu wsiadasz na statek i płyniesz parę godzin (około 3-5) więc najlepiej wycieczkę zacząć bardzo wcześnie by wieczorem na spokojnie wrócić :)

There are ferries twice a day (at noon and some time in evening 10pm as far as I remember). Both to Ystad / Sweden. It takes 7 hours to get there. Unfotrunatelly 10 years have passed since duty-free shops and bars are no more due to EU integration. ;-)

Check here for details: http://www.polferries.com/prices_and_timetable

Hope it helps.