Croatia is a great destination if you want a good mix of nature, sea, mountais and party. We travelled around Split and Hvar island many years ago, arriving by train from Budapest (Hungary).
A good mix of nature, sea, mountais and party
Split
Split is a very nice city but I think 2 days are enough for a visit (St. Duje’s Cathedral, Pjaca Square, Peristil Square).

Peristil Square source: Vidiworld

Nörd The World is Beautiful: Croatia

Nörd The World is Beautiful: Croatia
Hvar island
Later we took a boat to Hvar island, a very nice place where you can find party but at the sime time wild nature. We enjoyed a good dinner in the old town and during the day we rented a car to visit other small towns and hidden beaches.
there was a dance club on the other Island many years ago, that you could access only with a small taxi-boat at night
If you want party, there are many bars and pubs in the Port (and there was a dance club on the other Island many years ago, that you could access only with a small taxi-boat at night).

Nörd The World is Beautiful: Croacia. Photo by Places of Juma

Nörd The World is Beautiful: Croacia. Photo by Places of Juma
Where to find more information
Here you have some links of blogs where you can find info: Places of Juma, The Crazy Tourist Split, The Crazy Tourist Hvar.