Our 20 year old twin daughters have the month of June to split between Croatia and Greece

You have 2 similar posts running. It would help if you suggest what their interests are or their goals for the trip - see historical sights or chill on a beach, go clubbing or adventure activities etc.

Most people on this forum are middle aged or older, so their perception of a good trip may not accord with with the ideals of 20 year olds. Get them to watch vlogs on YouTube for ideas.

You can easily spend a month in Croatia or Greece. The links between the countries aren’t great, as I recall flights to Athens don’t run every day.

3 days in Split, 1 week in Hvar, 2 days in Dubrovnik, 1 week in Rhodes, 1 week in Mykonos. That's what a 20 year old would want to do.

My 17 year old is going to Hvar for 8 days in June with friends and wants to hear nothing about my suggestions at all.

My favorite street in Zagreb is Tkalčićeva where your daughters will be able to find a nice place to sit and enjoy a meal. From Zagreb your daughters can take a direct overnight train to Split (5h 15m) and rent a sleeper car. Heck, you have to sleep somewhere and this saves time. They can also take the train during the day. Another option is to take a nonstop flight to Dubrovnik.
A nice way to work your way to Dubrovnik from Split is to take a ferry from Split to Stari Grad and a taxi to Hvar (1h 15m). From Hvar take a ferry to Korčula (1h 15m). From Korčula take a ferry to Dubrovnik (2h) and a bus to Dubrovnik – Pile (15-minutes) that’s a 5-minute walk to the old town.
While in Dubrovnik your daughters need to stroll the Stradun (old town), walk on top of its wall (City Walls) and ride the cable to Mount Srd.
From Dubrovnik your daughters can fly nonstop to Athens and spend a couple nights and visit the Acropolis and museum, the Ancient Agora and the National Archaeological Museum. From Athens they can fly nonstop to Santorini or Mykonos. From Santorini or Mykonos they can ferry over to Naxos that’s located in the middle of these islands and then on to the other. The ferry from Santorini to Naxos takes 1h and from Naxos to Mykonos 45-minutes.

Marissa, what an exciting trip for your daughters! And what memories they will create together! But Jennifer is right that it’s hard to suggest things out of the blue without knowing anything about them, their experience, or preferences. Do they prefer outdoor activities, water or mountains, etc.? The good thing is that whatever they do (unless it is just sleeping in every day) will most likely create in them a desire to travel more as they get older - so in that regard, there are no bad answers. But a good general idea is to head toward Split, then time on an island, before Dubrovnik. I assume they will be confined to public transportation getting from Zagreb to Split. Ferries will get them to all the other places.

And I will say when my daughter did her first solo trip at that age, she did lots of her own research and planning but she also absolutely wanted to talk it over with me and get my ideas - it was part of the pre-trip fun and a wonderful memory we share. Nearly 10 years later she teaches me things but we still love to talk trips.

To me Plitvice Lakes National Park is a really special place. It should appeal to 20-year-olds as much as to older folks. The trick to really enjoying it is to spend the night in or near the park so it can be visited outside of the totally swamped daytripping hours. Ideally one would arrive by mid-afternoon and see some of the park before it closes, then finish up the next morning before moving on. You can see a great deal of the park in 4 hours or so.

There's bus service from Zagreb and (probably not as frequent) bus service on to Split. Booking.com probably lists some lodging options outside the park; some may offer transportation to the park. The hotel(s) inside the park are rather pricey, and I gather they are no great shakes.

A tip about Croatian buses: It is perfectly legit for the driver or another bus-company employee to charge the equivalent of about $1 to stow a bag in the luggage hold. It is not a scam.

I’m not sure of the importance of knowing about your daughters to give suggestions. I figure it’s up to you and them to sort through the suggestions and see what interests them rather than for us to filter out what we think they would like. I’m just going to go off of my own opinion and you can take it as you will. I would definitely suggest they take a bus from Zagreb and spend one night in Plitavice NP was definitely a highlight of my trip. They could easily either spend one night there or use it as a stop over on the way to their next destination as there is a luggage room at the park.

Zadar is a cute city that I think shouldn’t be missed. Less crowded and cheaper than Dubrovnik and Split, still full of ancient ruins, and it’s riva has the best sunset every night.

I would completely skip Krka if they are going to Plitavice. Split is a fun city and a party town. Decent amount of beaches for a swim and very touristy. But there are a lot of day trips that can be done from the city so it’s a good hub.

I went on a sailing cruise for 8 days along the coast and visiting Dubrovnik, Mijet, Makarska, Korcula, Hvar, Omis, and Split. If they love adventure sports, they should stop in Omis. The town itself is the size of a pin drop but they offer everything from zip lining, to canyoning, to kayaking. Hvar is quite the party island and they will probably enjoy a few days on the island, Carpe Diam is a huge tourist trap club but I think one two twenty year olds would need to experience. Korcula was cute but I was bored after an hour. Makarska was probably my favorite location. It was just a nice vice and they had parasailing and an inflatable park on the water. Dubrovnik is a must see, however I just found the tourist tax a bit too high in the area for me to really enjoy the place.

If at all possible, your girls should look into traveling to Mostar and Kotor during their trip. Mostar can be visited when traveling between split and Dubrovnik and Kotor is just a 3 hour bus from Dubrovnik.

Hi, I've cleaned out a side issue that was brought up in this thread. I'm addressing this privately at present. Thanks, everyone!