Croatia trip

It's not really possible to offer feedback based on your very scant description of your itinerary.

Can you provide more details? Where are you flying into and out of, and where do you plan to go besides Split, Plitvice, and Ljubljana?

This forum is much more helpful if you have a more specific idea of what you want to do. Your post is much too broad. The Rick Steves Croatia & Slovenia guidebook is really what you need here. This region has a lot of sightseeing options and getting around can be challenging. This is all stuff only you can figure out with the help of a good resource book. Then, folks can help you fine tune your itinerary.

That aside, fly to Brussels, probably from Zagreb which is likely cheaper than Ljubljana.

I'll add to Geoff's report with my own from 2022, in case you might find it helpful.

https://community.ricksteves.com/travel-forum/trip-reports/croatia-and-ireland-may-2022-castles-and-forts-and-water-oh-my

I agree with posters who say we need more information to be really helpful. Where will you be before Split? Are you renting a car? If not, I highly recommend renting a car. Driving is very easy in Croatia, and will make getting around much easier.

I recommend 3 or 4 nights in Split. We stayed 4 nights. Took the catamaran to Hvar Town for a day. Visited Trogir for 3/4 of a day. We love Split. It's beautiful architecturally and has a lovely location on the Adriatic. We hired Maja Benson, recommend by Rick, for a 2-hour private guided tour of Old Town and Diocletian's Palace. She is worth every penny. We enjoyed the Ethnographic Museum. Drinks on the Riva.

We spent 1 night at Plitvice Lake NP. Visited the Upper Lakes in late afternoon on arrival day. And visited Lower Lakes the next morning. Then around noon we drove to Zagreb where we returned our rental car. Spend 2 nights in Zagreb. Then took the train to Ljubljana for 3 nights. Rented a car for a day to drive to Lake Bled. Hope this helps a little bit.

Ok!! I am flying from London to Dubrovnik and staying there 3 days, visit Montenegro one day, then going to Korkula for two days via ferry??… going to Split for two or three days, rent car there (any suggestion car rental?) leaving for Plitvice lakes 2 days and from there to Ljubljana and surroundings. No sure what to do with the rental car. We will go next to Brussels and not sure yet how if go back to Zagreb or from Ljubljana. I would love some advice and hope this time I am giving more info. Thank you

Last week of September things might be winding down on the coast. You can check the ferry schedules at croatiaferries.com which shows all lines from various companies (no real difference between them.) You really only need one night in Plitvice. The formula for visiting efficiently is often discussed in this forum. You can get a sense of it here, but really the RS guidebook breaks it down the best.

Dropping a rental car in a different country comes with astronomical fees. Your best bet will be to drive to Zagreb, and either bus or train to Ljubljana. Buses are good here. Go to getbybus.com for schedules. Ljubljana airport is expensive to fly through, so many people use neighboring airports in Zagreb, Austria, or even Venice. Hope that helps.

All the posts are giving good advice. I will add that the ferry/port/bus terminal
area in downtown Split can be incredibly crowded. It is not the place I would
choose to pick up a car and start driving. In addition, you will eventually need to
head east to the main highway to get out of Split to drive to Plitvice. So if you
can find a rental car place away from downtown, it's probably worth the bus
ride or cab fare. I used the Sixt location on Polijcka cesta, no problems.

If you have a car, picking a place to stay in Plitvice for one night is somewhat
arbitrary. My impression is that most places are simple but clean accomodations.
You don't have to stay at the Jezero if you have a car.

Also note that down in Rudanovac, at the intersection of 1 & 52, there is a full
service grocery store. Useful for breakfast if your lodging doesn't serve it, so
you can get an early start on seeing Plitvice.

I would consider spending a night in Zagreb - it eliminates the dropoff charge for
the car as noted before and Zagreb is a fine city for a day or two in and of itself.

If you don't have a flight out yet, it could make sense to keep the Croatian car for the Slovenia portion of the trip, then drive the 1.5h to Zagreb to drop off the car back in Croatia (and saving the $500 fee to drop off in another country) and flight likely more and cheaper flight options to Brussels. I had a good experience renting from Nova car, they seem to be the most recommended and reliable for Croatia. We dropped off in Split at the port and had some stress finding the drop off location (one-way streets and having to loop back again, would be less stressful picking up there vs dropping off). We picked up at the Zagreb airport and it was a breeze (airport was smaller than expected).