Bicycles are easy to rent along the coast and on the islands, and cycling can be a great way to explore the islands. Relatively flat islands such as Pag and Mali Lošinj offer the most relaxed biking, but the winding, hilly roads on other islands offer spectacular views. Cycling on the coast or the mainland requires caution: most roads are busy, two-lane highways with no bicycle lanes.
Some tourist offices, especially in the Kvarner and Istria regions, have maps of routes and can refer you to local bike-rental agencies.
If you have some Croatian-language skills, www.pedala.hr is a great reference for cycling routes around Croatia.