The Danubiana is a museum of Modern Art located at a river bank of the Danube in the south of Bratislava, at a quarter called Čunovo. In my opinion it is one of the best modern art museums, one that didn’t disappoint me (and I’m often arguing about the works exhibited in those museums).
The art works on display are amazing, the building itself would be worth coming here: you can watch the close-by river through huge windows. On top of the building is a nice statue park and you can have a walk in the fantastic garden including a good coffee bar.
You can reach the Danubiana by boat, but if your travel plans don’t fit to the timetable you should consider renting a car. Going there by car is fast and easy, but you should check the route of your navigation system: car rental companies often only supply vignettes for Slovakia.
If you are going one exit too far you are on a Hungarian motorway and would need a vignette from Hungary. But the next exit is only 300 meters away and hopefully no one will find out. 😉 The correct exit within Slovakia is Rusovce.