Slovenia & Croatia - 8 days

I think it's smart to limit yourselves to 3 destinations in 8-9 days, and while there are, as you say, a lot of options, there's absolutely nothing wrong with the ones you're proposing.

Be aware that all these destinations will involve a fair amount of walking if you want to see a lot of sights. Fortunately, they are also fine places to grab a table at a cafe and enjoy the ambience, so you should have no problem pacing yourselves.

Enjoy!

Good planning for this trip.

1) I'd train from Ljub -> Zagreb. Train station is right downtown. Of course, the bus station is as well. Both are on the tram line. Trams cost 4 K/ride (about $.60).
2) While both towns are walking based, downtowns are small and very easy to get around in.
3) In Ljub - do the castle. Also there's 1 tall building and a cafe on the top floor - that's fun
4) In Zagreb - there's the upper town and the lower town. You can walk up or take the funicular - cheap. Museum of Croatian Naive Art is my fav. Take time for the market in the middle of town as well.
5) Flying to Dubrovnik is probably the best idea with your timeframe. Walk the walls. Spend time in the town more in the evening - tour boats tend to saturate the town.

Have fun. We love Croatia.

Sounds like a great itinerary for 8-9 days. I would second Paul’s plan above.

Ljubljana is our favorite city in Europe. All pedestrian friendly and also offers the Kavalir. It’s an electric-powered vehicle as a transport option around town. It’s free. Friendly to people and the environment. We stayed 4 nights and didn’t want to leave. I can recommend our favorite restaurant: Julija. We ate there 3 nights. Reservations are a must. Yes, visit the castle per funicular. Enjoy the wonderful open market in town. Visit the Plečnik House Museum, home of Architect Jože Plečnik, famed for buildings in Ljubljana. Stop for the best gelato at Gelateria Romantika. Sit at a cafe by the River and enjoy the ambience of Ljubljana.

Lake Bled makes a nice half day excursion. We enjoyed walking the lake & having lunch.

We stayed two nights in Dubrovnik with a guided morning tour of the old town. Our favorite restaurant was at Kazbek Hotel. Location is in Lapad near old town. kazbekdubrovnik.com Best meal we had in Croatia.

We flew to Zagreb from Dubrovnik for a brief layover. We would have stayed a few days if we had more time.

I'd make the train-vs.-bus decision on the basis of schedule. I doubt there will be enough difference in cost to matter. I believe ther are considerably more buses than trains. Certainly the Zagreb bus station was a comparatively busy place back in 2015, whereas the train station wasn't. I took the bus; it was fine.

Thanks all so far!

Another question -- I was wondering about Zagreb. I've read some don't feel like it's worth the time in a time-crammed itinerary (like ours) but others say it was a delightful surprise. Is it worth stopping over for a day-and-a-half as in the above itinerary, or would it be better to skip it altogether and extend both Ljubljana and Dubrovnik by a day each? That would essentially mean 3.5 days or so each for Ljubljana/Bled and Dubrovnik.

Thanks so much, super helpful so far.

This site may give you some insight for 36 hours in Zagreb.

https://www.apieceoftravel.com/zagreb-itinerary/

Try to take that 2:12p train departing Salzburg Hbf station arriving in Ljubljana at 6:32p (4h 30m) since it’s direct. The other trains require a connection.
Your itinerary is the same as mine when I went. I took a direct train between Zagreb and Ljubljana (2h 30m). There is a direct train departing Ljubljana at 8:30a and 2:45p (2h 30m). I checked the bus schedule for Aug and only saw evening departures.
You asked if Zagreb was worth it, yes it is and do stroll along Tkalčićeva Street.

Lake Bled is a beautiful and relaxing place. Perhaps your mother would enjoy a night or two there on the way to Ljubljana. You will still have 2 nights in the latter to enjoy and no backtracking. I've not been to Zagreb or Dubrovnik but might be tempted to add another night in Ljubljana and day trip to Zagreb. Then you'd have at least 3 nights on the coast in Dubrovnik. BTW Rovinj in Istria is great so you could trade it for Dubrovnik and still get to the coast without the hassle of flying during your trip.

Be sure to treat yourselves to the cream cake on Lake Bled.

Thanks all so far for the comments and tips! We're leaving the schedule as-is. Based on all of your comments it seems like it will be a good way to see a few main and varied cities within the two countries.

Hotels are booked, now working on walking tours and things to see/do in each place.

@waitruserious I would love to hear how your trip goes and hear your thoughts on Zagreb as I've heard the same conflicting opinions (and Ljubljana, too). I'd be especially interested in your experience boarder crossing between Slovenia and Croatia. We leave the last week of September for Croatia, starting in Dubrovnik and moving northwards through Zagreb, ending in Slovenia. Safe Travels!

@Rena, we just returned from our trip. I loved Zagreb! It's small but has a lot of character. I recommend a walking tour (I chose this one from GuruWalk: https://www.guruwalk.com/walks/154-free-spirit-walking-tour-zagreb). The outdoor cafe/bar scene is some of the most popular and lively I've seen. I can also highly recommend staying at Hotel Dubrovnik, which is literally on the main square of Zagreb.

Ljubljana is also nice -- quaint, small but also a lot of character and fun to explore. Also a great outdoor scene. I wouldn't mind revisiting either city, though both can be seen and explored in just a couple days.

Border crossing from Slovenia to Croatia was pretty smooth. We traveled by bus across the border. We were all required to disembark and show our passports when leaving Slovenia, and then again just a bit further down when entering Croatia. What I can say is that the border traffic going the other way (Croatia into Slovenia) was a lot. Wouldn't have wanted to be in that line, but Sept/Oct will have fewer tourists so likely better for you. The weather will no doubt be cooler as well, perfect time to go. Enjoy!

PS - Croatia has an entry form. It didn't seem vitally important when crossing but it's easy enough to fill out just in case https://entercroatia.mup.hr/