"Beach" does not necessarily mean a large, open, sandy area leading to water for people to lay out, swim, play volleyball, etc. That's what I picture, what I assume, when I hear that word. Rovinj, Santorini, Cinque Terre (and more) prove otherwise).
Rovinj has beaches, but not Beaches. I'd categorize them more along the lines of swimming holes... They say beaches. On our side of Old Town Rovinj, there were two main swimming holes/beaches. These areas were filled with locals (old, young, really old, really young) - spending their day off or just their lunch break. Pick a flatt-ish rock (or concrete slab) depending on which swimming hole you're at. Lay out. Swim.
Along Zlatni Rt National Park there were thousands of swimming holes and these swimming holes were being used. Since you could only get there via bike or foot, the path was lined with the parked bikes of those visiting. Same thing. Pick a flatt-ish rock. Lay out. Swim. Here there was also more snorkeling. Zlatni Rt National Park is lined with trees, huge, old, beautiful trees (the park hosts 10 different species of Cypress Trees), so you can choose between sun and shade... and when it's 36C outside, trust me, you want that option.
These swimming holes are rocky underneath, not sandy (chacos would be a good idea). There is no sand. But, you can layout. You can swim. It's a beach.
Another little guy taking full advantage of the awesome swimming holes
Old Town Rovinj swimming hole
See... Beach. You lay out. You read. You jump in the water. No sand here.
Swimming hole right near our apartment.. I'd say my favorite of the 3 or 4 we visited
View from one of the many swimming holes along Zlatni Rt National Park, Rovinj
Swimming hole in Rovinj, 2 minutes walk from our apartment