Having just done this a few days ago, I’d ask how much time you have and what your interests are. In Istria, we stopped at Buzet, which has a silent, ancient old town surrounded by a small city. I’ve read that there’s a town called Dvrograd, about 20 minutes from Rovinj that’s an abandoned, ancient town. We didn’t have time to search it out, but if you do, please let us know how it was. I like Groznjan. It’s pretty and green, if a bit heavy on the truffle shops. Outside of Livade, there’s a restaurant called Konoba Dolina that’s very good. Continuing on the highway, we had one toll for 33Kn. From there we used google maps, which took us crazy out of the way, but if you’d like to see some war ruins (damaged, abandoned house with lots of bullet holes), try Plaski and Liska. Be aware that this route also covers lots of back roads, which can be very slow. This route also took us in the back way to the park, so we saw a lot of wooded hills, and had a few hair raising episodes with trucks on one lane roads hugging cliffs. Some people love that sort of thing.... Opatija was our overnight stop from Rovinj to Plitvice, but we didn’t do anything special there. It was easy to get to the “centar” where the big hotels are, but confirm yours has parking.