As a matter of fact Bratislava isn't must see in Europe but there are some sights here: Old town, St. Michael's Tower & Street, Castle of Bratislava, Grassalkovich Presidential Palace, Danube embankment. It's enough for 1 day to spend all the rest time you may join cultural events or festivals, drink slovakian beer and eat local food for low prices and go shopping. It's really nice place to visit! Have a good trip :)