There are many good agencies offering trips etc. Check www.istra.hr for extensive list.
We booked trips through our Thomson rep but found that boat trips, including Venice, could be done for a lot less by booking with the "boat people" on the seafront. You can't miss them :) I'd certainly shop around for the other trips. I've done most of them but would recommend the Postojna caves and the Lipica stud farm in Slovenia. They can be done in one trip. Not for people with mobility problems though.
Thank you for your post about Lipica Stud Farm. Did you take a tour, or go on your own??
We took a tour which included the caves, amazing! Lunch was included. The caves are a 1.5 km wet and sloping walk underground after a thrilling train ride but so worth it, then on to the stud farm where we had lunch. That included a display by the horses and riders in the indoor arena (tears to my eyes), the "stampede" then a guided tour of the stables. It's a long day but something you're unlikely to encounter anywhere else.
Thanks Jenny. These are two trips I would be interested in.
Thanks for your tip
Škocjan cave is another option if seeking a less commercial adventure. Absolutely breathtaking!
Easy to rent a car to take into Slovenia for more flexibility if you like.
Well worth doing. You can do both places in the one trip.
Thank you for your information! I will take your suggesions.