Any help with itinerary would be appreciated

Dropping an Italian car in Slovenia would almost certainly incur a very high international drop charge--hundreds of euros.

How well do you handle the jetlag and deprivation of an overnight flight? I adore Venice, but hotels there are rather expensive. I'm zombified on my arrival day and barely functional the next day. It wouldn't make sense for me to spend just one night or two nights in Venice at the beginning of a trip.

I've never tried to connect Venice and Ljubljana, but I know from reading others' comments that GoOpti runs both private and shared shuttles from Venice to Ljubljana. Flixbus operates on that route as well and would be less expensive. By train you could easily get to Trieste, but then you'd want to switch to road transportation. The options I'm aware of are GoOpti's shuttles and buses operated by Flixbus and ITAbus. I think ITAbus is the cheapest option. At least some of the buses pick up at multiple points, so you'd need to research which is most convenient to the train station in Trieste.

Ljubljana is a charming city but not terribly large, so with five days you could probably do multiple day trips or spend part of your time elsewhere.

I should point out that Budapest is a much larger city that justifies a considerably longer stay. Have you been there before? If not, I'd want to spend a bunch of days there before embarking on the river cruise.

I live in the region (Budapest) and have not yet been to Slovenia. Was thinking about it for early this summer. One of the reasons I havent been it that from Budapest to Slovenia is a long haul without a lot of “to die for” stops along the way. There are no direct flights, and the train is 8.75 hours or for about 400 euro there is DayTrip.com that will make the trip in 4.5 hours, and if you want there are some stops along the way, but none that lit my fire.

Ljubljana looks lovely and I could probably be happy there for two nights, maybe 3 if I have a late arrival. Bled you go for the view I guess and so two nights would be enough. I’ve been to Zagreb and enjoyed it and its good for a night or two. But in my book these are all interesting but not to-die-for experiences. So, again, it looks like my trip to Slovenia is getting shoved aside by a fourth trip to Slovakia and a fourth trip to either Bosnia or Montenegro (depends on some hotel reservations and some fly fishing guides availability).

Better connected to Budapest, If you like the outdoors, the coast, sea food, mountains, rivers and maybe rafting ….. then Montenegro is a good choice. For castles and interesting villages and mountains then Slovakia. For a real cultural experience then Sarajevo (not quite as well connected, but worth it). I don’t know where you are coming from, but if your city is served by Turkish Air, then travel direct to Budapest but do their free layover tour of Istanbul on the way.

Or Slovenia if it lights your fire. And if you do, I would just bite the bullet and take the train.

Thank you so much for your thoughtful replies. I guess I should rethink Slovenia this time around. I have never been to Budapest before or Slovakia. Will spend some time to check them both out. I just saw a video on Slovenia a couple of years ago and was hoping to get there on this trip. I

f I was dead set on going to Slovenia (which is not the case) would reversing the direction of the river cruise be any more helpful?? Starting in Passau, Germany, versus Budapest.

Thank you again for imparting your experiences and recommendations.

The whole river cruise thing is also new to us so it will be an adventure regardless.

I wasnt trying to talk you out of Slovenia. You can search the forum and find hundreds of great reviews of trips. Just hasnt risen to the top of my list yet as there are too many other places that for me, right now, seem more exciting.

If you reverse the cruise you can fly straight to Zagreb or Ljubljana. There are plenty of connecting flights, most seem to go through Munich so I suspect you can do it from the US with one change in Europe. Then to start your cruise the flights from both Zagreb and Ljubljana to Munich are fairly inexpensive and only take about an hour.

When you arrive in Budapest, do allow yourself 3 full days of sightseeing. Thats a minimum and 4 days is probably about prime for a first trip. But if you find yourself with less, do let me know and I will give you some suggestions to get the most out of it.

Getting back to the states from Budapest is fairly easy......

Here is someone doing 10 days in Slovenia. You might get something out of their plans. https://community.ricksteves.com/travel-forum/slovenia/slovenia-for-12-days-family-trip-in-june

While hotels out on the Venice islands are very expensive, there are some very affordable options on the mainland near the train station there. Look for hotels that advertise as Venice Mestre. There is even a train option to get from Venice to Ljubljana, Slovenia if that works well for you.

You can also take trains between Budapest and Ljubljana. Rail Europe is showing me two options with the shortest taking 10 hours and involving 2 changes. One change is in Vienna and the other is in Graz.

It would be by far most economical to go with trains for the travel between countries then just rent a car in Slovenia.

Dont use Rail Europe for your research. You want to go the Slovenian and the Hungarian rail sites and look. There are direct trains and trains with one transfer and the times are as little as 7:30 (but do check transfer times as some appear a little tight). Of course I just checked a random date in April.

You also might look at a direct train out of Zagreb that makes the trip in about 6 hours.