There is a very extensive bus newtwork in Croatia and the cheapest form of transport. From Zagreb, take a bus to Varazdin, quicker and cheaper, from Varazdin train to Koprivnica and another train to Osijek, from Osijek visit Vukovar (by bus) and bus or train to Zagreb, from Zagreb freq. buses to Plitvice, from there to Zadar, from Zadar by bus to Split and Dubrovnik. Visit nearby islands, if possible.