festivals
Karlovacki Dani Piva
end of August
Annual beer festival. The most crowded place at that time of summer, with various folks around. You can grab a beer and pretzel and see if there's a music which suits you.
Swimming / Rafting / Kayaking
Great swimming in summer months in Karlovac rivers Korana and near by Mrežnica with rafting and kayaking.
Mountain Biking
Mountain biking is recommended. Lots of preserved trails all around the city and enthusiastic bikers who'll gladly guide you.