What are the best (beginner) adventure activities for a Croatia vacationer in September (biking & boating esp)

Question

We haven't really done much kayaking, mountain biking, etc. So we're definitely at a beginner level. Also open to renting a motor boat/wave runners. We're spending two weeks in Croatia, divided between Plitvice, Hvar, Split, and Dubrovnik (although we're open to detours:) Mid September time frame

Answer 1

Find a windsurfer.  My friends all waterskied.  The water will still be ok in Sept./