The KopaÄki Rit (http://en.wikipedia.org/w...) is the biggest natural wetlands in Europe and the birdlife is spectacular. This enormous nature park, located around 15km north of Osijek where the Danube and Drava rivers flow into one another, is a great day out in the countryside - though bring some insect repellent as the mosquitos do bite!! There is no public transport to the park, so take the local bus to Bilje and its a 2-3km walk.
itineraries
Stay in Osijek, the principal city of Slavonia and visit all the sights and cities around.