The main islands in Kvarner are Krk, Rab, Cres and Losinj. There are numerous smaller islands, most of which are uninhabited. The sea kayaking potential is enormous and relatively unexplored. Even in the height of the summer season it is normally possible to find your own beach with the help of a kayak.
The calm seas in the summer make the egio deal for exploring with an inflatable kayak. This option also has the advantage of making one way trips possible with the use of buses to ad fro the start points.
While the potential for outdoor sports is more limited than in the high mountains, there are plenty of potential for biking and hiking. Most tourist offices produce maps of the marked routes. They are available for free in most tourist offices. I have provided scans of the maps on this page for advance information.
The quality of mountain bikes on the islands available to rent has been improving over the last few years, but many very cheap “mountain bikes” are still being rented out. Below is a list of better quality bikes available for rent. It is rare that pumps and repairs kits are provided. I suggest you bring your own. Helmets are often but not always available. Several places rent bikes with child seats.
True sea kayaks can be rented in Omisalj on Krk, and in Rab town, on the island of Rab. The website of latter is useful resource for potential routes.
The kayaks from Omisalj can only be rented after joining the local rowing club, this is due to Croatian bureaucracy and is not intended to exclude potential paddlers. The details are on their website.
Sit on top kayaks can be rented in on almost all tourist beaches. These are usually in reasonable condition and adequate for day tours or even longer. Life jackets are usually available but you may want to bring your own dry bags and any specialist clothing.