Slovenia/Croatia

If you've been to Europe before, Slovenia and Croatia are relatively easy to see on your own. I've done solo trips there a few times, and I have found getting around very easy; I found the ferries the most challenging part to figure in on my first trip, but you won't have to deal with that. Plitvice goes well with Slovenia, although if you drive a rental car across the border, you sometimes have to worry about delays at border crossings. Not really an issue if you take trains between Slovenia and Croatia.

If you have enough time, you can certainly add Mostar (and Sarajevo?) and Split. Assuming you have a rental car, you could drive from Plitvice to Sarajevo to Mostar and back to Split and fly out of there - Split has a good number of budget flight connections to other European cities. The drive between Sarajevo and Mostar is breathtaking in parts along the river, and there are a few interesting spots in Bosnia you might want to stop (at least for a few hours) between Plitvice and Sarajevo (like Jajace and Travnik).

Logistically, you could start in Ljubljana, train to Zagreb, rent a car and drive to Plitvice, Mostar, Split, etc. and return the car in Split or somewhere else in Croatia. (Returning a car rented in one country in another usually incurs a steep one-way drop fee.) Doing this by public transportation is possible but much more of a hassle, mostly by bus once you get to Zagreb.

Thanks so much for your reply, Andrew. I never thought of taking a train to Zagreb and then renting a car. I'm glad you have done this solo yourself and didn't find it a hassle. You are correct; it is easier to pick up/drop off a car in the same country. I'll have to get a good map and see how far these places are from one another. Thanks again!

You can check Google Maps for driving distances (but pad the estimates slightly). Zagreb to Plitvice is about a two hour drive.

You can drive Plitvice to Sarajevo in a day, but it's a fairly long drive. I met up with friends in Sarajevo who did it (we both drove the other direction). I left Sarajevo for Plitvice a day before them and stopped for a night in Jajce in between; they stopped in Jajce for just few hours and pushed on to Plitvice. The roads are fairly good in Bosnia now (even if not as good as Croatia's) and it's easy to drive there.

Sarajvo to Mostar is an easy drive; Mostar to Split would be easy too.

We drove the from Dubrovnik (picked up car when ready to leave - do NOT want a car while in Dubrovnik) to Mostar to Plitvice to Ljubljana this summer. The driving is very easy. Taking a train then driving the rest of the route would work well too. I would not hesitate to drive in the countries again.

We've been to Croatia and Slovenia 4 times in the last 6 years - it seems like every time we go to Europe, we go to Croatia. Great country. You can do them on your own, NO PROBLEM. If you want to drive, Croatia has many nice roads. You can also get to Plitvice Lake Jezera by bus from Zagreb. You should include Zagreb in your trip. Good place to start your trip and to fly into. You can fly to Zagreb, take a car or bus to PL, go to Zadar or Sibenik, maybe Rijeka, drive to Ljubljana, and drive around no problem. Getting to Mostar is a bit more difficult. Some car rental places make it difficult. It's easy to get to Mostar from Dubrovnik. But also we have hired guides to drive us around, and it is amazingly affordable, or was 3 years ago. However, Split especially has lots of stuff you probably haven't done. There is the antiquarian museum, which has a ton of stuff. There is also the Roman ruins at Salona near Split. From Split, you can do day trips to Trogir and other towns. We've done all this on our own, either with a car or on trains/buses.

I was just in Slovenia in early September.
We drove from the Austrian border to Lake Bled and took a day trip to Ljubljana.
The driving in Slovenia is very easy. The main roads are in excellent condition. Parking was not difficult anywhere we went.
Navigating is not complicated either since things are rather small and it's very easy to find city centers and attractions.
While in Bled we really didn't use our car since everything is within easy walking distance.
We did drive out to one of the nearby gorges to hike - absolutely beautiful and worth going!
It is a very lovely country with great food and beautiful scenery!

Thanks for all of your responses. I have decided that I don't want to drive, especially since I will be by myself. This is my plan so far: Fly into Ljubljana. Four nights in Ljubljana. One day tour to Lake Bled. Train to Zagreb. Four nights there. One day tour to Plitvice Lakes/Waterfalls. Fly out of Zagreb.

I think Mostar will have to wait unless I fly to Sarajevo and take a day tour from there to Mostar. This would add a couple of days to my trip and I'm not sure if air connections from Sarajevo to the rest of Europe to fly back to the USA will be the best use of my time. I think I would have to fly back to Zagreb and stay overnight at the airport before flying to Frankfurt (probably).

Comments/suggestions about my itinerary are welcome. Thank you again!

Unless your trip is way off-season, I urge you to spend the night before your visit to Plitvice in or near the park. I did not do that. My last visit was in 2015 (it's probably worse now--isn't everything?), and my day-trip from Zagreb was seriously marred by crowding on the walkways. Think about the pictures you've seen of the Vatican Museums; it was like that. It is not hard to get a public bus from Zagreb to Plitvice so you can arrive in the mid- to late-afternoon and spend the night. I think you can find small lodgings outside the park but near it (if you want to avoid the extra cost of staying inside the park) that provide some sort of transportation to the park. There may be a few that are within walking distance. Booking.com is one place to look.

It's a simple, easy itinerary. Some people love Zagreb, but I am not one of them. I'd be bored with four nights there. Four nights in Ljubljana would be fun for me, because I love the city, and there are a lot of easy day trips - and it's a great place to come back to at night. I'm sure there are some good day trip options from Zagreb, too, besides Plitvice, but I'm not up on what the best options are.

If you aren't going to stay over in Plitvice anyway, instead of a day trip from Zagreb consider doing a trip from Zagreb to Split with a company that does a tour stop in Plitvice for a few hours. I know you've been to Split before; an alternative might be nearby Trogir, which is smaller than Split but charming. (Trogir is really close to Split's airport if you can fly out of there.) Maybe you could do two nights in Zagreb, do the day tour/stop in Plitvice on the way to Split, and two nights in Trogir or Split. (Disclaimer: I've never used a tour company that does the day stop at Plitvice - but I've heard of one, easy to find by googling.) Or, two nights Zagreb, take the bus to Plitvice and spend a night at one of the park hotels, take a bus south to Split/Trogir and spend the last night there. Assuming you have only eight nights.

I do like Zagreb and could fill 3 days there (4 nights) because there are so many (and varied) museums, but I'd recommend 3 nights for the more typical traveler Which fits well with one night at Plitvice. In truth, except for Plitvice (mistake!) I've never made a day-trip from Zagreb, so I don't know what the attractive options are. Aside from Ljubljana, of course, but that's more than a 4-hour round-trip we're all agreed that it's worth a multi-day visit in its own right.

Why was Plitvice a mistake?

Plitvice gets mobbed with tour groups during the day, especially in season. I'm not sure you mention time of year you plan to travel. A day trip in July would be a lot worse than a day trip in October. If you spend a night at Plitvice, you can enter the park first thing in the morning and experience it without the mobs of people at least for the first few hours.

I did stay in one of the overpriced Plitvice park hotels a few years ago (but I had a car). It was very convenient to the park - just walk right in. Driving yourself would mean parking further way from the park entrance than it is just to walk in from the hotels. If you want to explore the park on part of two different consecutive days, the park hotels can stamp your park ticket from the previous day so you don't have to pay the entrance fee for the second day.

Sorry for being cryptic. I meant that visiting Plitvice on a day-trip from Zagreb was a mistake. It's a great, great destination, but it is far more popular now than it was on my first trips back in the 1980s/early 1990s. You really, really need to be there when the daytrippers are not.