Zagreb, interesting church roof
Istria peninsula, Motovun, Parec, Rovinj, Pula, Opatija
Several islands, Krk, Rab, Hvar
Plitvice lakes, drive inland with lots of destroyed houses, new houses built next to it. Amazing lakes and waterfalls, nice boat and hike around the park.
Sibenik
Dubrovnik, old town, walk on city walls all the way around, if you want to, you can stay in Cavtat, much cheaper and easy boat trip to Dubrovnik, you can do a day trip to Montenegro, southern most fiords of Europe.