Dubrovnik
The old city of Dubrovnik is enclosed by medieval walls that you can walk in their entirety — about two kilometres with views over orange rooftops and the Adriatic. It's genuinely one of the most beautiful cityscapes in Europe, and heavily visited as a result. Come in May or October if you want to appreciate it rather than fight through it. The cable car ride up Mount Srđ gives the full panorama.
Plitvice Lakes National Park
Plitvice is Croatia's most dramatic natural attraction: sixteen terraced lakes linked by waterfalls, surrounded by forest. The colours shift from turquoise to deep green depending on light and season. Boardwalks allow you to walk at water level beside the falls. Go early, book tickets online in advance, and avoid mid-July if crowds bother you. The park is in inland Croatia, easily combined with a drive between Zagreb and the coast.
Split
Split is built inside and around Diocletian's Roman palace — an extraordinary thing, a 4th-century imperial complex turned into a living city where people hang laundry between columns. The old town has restaurants, bars, and markets within walls that were built in 305 AD. As Croatia's second city, it also has good museums, nightlife, and a working-port energy that Dubrovnik lacks.
Hvar Island
Hvar has two reputations: a party island for the summer jet set, and a beautiful Dalmatian island with lavender fields, olive groves, and a dramatic 13th-century fortress above the town. Both are accurate. Hvar Town is lively and expensive in July; the rest of the island is quieter and worth exploring on a scooter.
Rovinj
Rovinj in Istria is a working fishing town with a remarkable setting — a peninsula topped by a baroque church, surrounded by an old town of narrow lanes and colourful houses. It's popular but less overwhelmed than Dubrovnik. The local Istrian cuisine (truffles, olive oil, fresh fish, malvazija wine) is among the best in Croatia.
Trsteno Arboretum
Near Dubrovnik, the Trsteno Arboretum — one of the oldest Renaissance gardens in this part of Europe, founded in 1492 — sits 20 kilometres up the coast and makes an easy half-day escape from the old town.
Korčula
Korčula is a compact medieval island town that claims to be the birthplace of Marco Polo. Whether or not you believe that, the old town — a grid of herringbone streets inside stone walls — is genuinely lovely and quieter than most Dalmatian destinations. The island produces excellent white wine (Pošip and Grk).
Krka National Park
The waterfalls of Krka National Park are more accessible than Plitvice and allow swimming at the base of some falls (Skradinski Buk). The park is near Šibenik, which has a remarkable 15th-century cathedral and is worth a half-day on its own.