Istria to Lake Bled (or Ljubljana) itinerary help

the distance is not long in between, but i think the places you mentioned are all worth a good look. i like piran a lot, the old town is really interesting to explore and if you hike up the hill the view of the city is wonderful. i also recall piran is a few hours by bus from LJU, so maybe it's not that close. so i think if you save the cave for a 2nd day driving to bled would be better. LJU is small but can be interesting to walk for a couple of hours also.

That sounds like too much for one day - your list looks like 2 days to me, at best. The Julian Alps loop takes most of a day to do unless you want it to be a nausea-inducing blur. We were there last year in May, and we experienced some weather - intense thunderstorms when we were in Bled, which some thought would have closed the Julian Pass roads due to snow. Turned out we dodged that bullet, but be prepared for wildly inconsistent weather. We also got a ton of rain in Istria (Motovun and others). We also got some rain (and some beautiful sunshine) in Rovinj. Despite the rain, we loved the area (we stayed 2 nights in Rovinj and one in Motovun). Had one of the best meals I've ever had in Motovun. Don't skip Pula - it's absolutely worth a couple hours, and is not too far out of the way from Rovinj if you have a car.

David(s), Thanks for both your replies. You confirmed our thoughts. We will adjust our itinerary to make it doable.
What do you think of driving from Rovinj to Piran, through the Karst, stopping at one of the caves on the way to spend the next 2 nights in Bled? Then we plan on driving a loop through the Julian Alps to LJU.

Caveat #1: We were going south, and we dropped our "Solvenia car" in Portoroz (near Piran), took a bus across the border from Portoroz to Rovinj - so for part of the way I probably have an inaccurate sense of how long it would take to drive. That said here's what we did: (we had a rental car) got up in Bled, drove to Predjama cave for a quick look from the outside (didn't go in), went to nearby Postojna cave, did the tour (surreal, and worth doing, but pretty strange). Continued south to Portoroz (very near Piran, it's the next little town over). Portoroz worked for us because it had 1) a car rental agency, and 2) a bus stop. We arrived in Portoroz about 1 or 2 pm, had several hours to kill there waiting for the bus. Took the bus south across the border into Croatia. Bus stopped several times en route, eventually dropped us in Rovinj; we arrived there around 6 pm? So, the drive from Rovinj to Piran, to the caves (stopping to tour one), then drive on to Bled should actually be very do-able in a day. The Julian Alps loop is most of a day, but returning to LJU after the mountain loop is not significantly further than just returning to Bled. Caveat #2: If you have not checked yet, be sure to investigate what you're going to be charged to rent a car in Croatia and drop it off in Slovenia - there's usually a huge "drop-off" fee. In order to avoid that, we orchestrated a somewhat elaborate scheme to rent two cars, one for each country, dropping the first one then crossing the border, picking up another and moving on. Complicated, but saved us a big pile of Euros. Hope that helps.

David, Thanks for your comments. I should have mentioned that we will be swinging back into Croatia at the end of our trip so we will be avoiding the fees for dropping off the car in another country. We plan on picking up the car in Split, and returning it before we fly out of Zagreb.
We will be doing the Rovinj to Bled drive through the Karst, then spend a day in Bled, then through the alps to Ljubljana, then to Zagreb for the last stop.

Sounds like a reasonable plan. Hope you are including a stop at Plitvice - it's well worth a few hours.

Most definitely. We plan on spending one night there between Split and Rovinj, which seems to be enough.