If you're staying on the Istrian coast then an excursion to Motovun (30-40 minutes away) makes for an enjoyable couple of hours. My suggestion would be look for a few other interesting hilltop villages and make a trip combining them.
The problem with Motovun is its size, it's a very small village and once you have walked the defensive walls, stopped in the village square for a drink and mooched around one or two of the many shops selling local wine, you're struggling to keep yourself interested.
Possibly the best thing about the village is view from the approach road, where the walled village sites magnificently on top of the hill and surveys all around it.
A word of warning for the less mobile, cars, busses and taxis are not allowed up the final stretch that takes you into the village and it's quite steep and, being cobbled, quite uneven too.
It is lovely, just don't expect too much.