September is just around the corner, probably first rains will signal that summer is going to its end. Of course, swimming season in Dalmatia will go on till the late October, but temperatures will drop for a few degrees and open a season of some other types of enjoying nature than just dropping on some beach. Meaning, go hiking!
Of course, lots of people go hiking during the summer, but Dalmatian mountains are tough, mostly rocky and sometimes you can feel like being in an oven up there. That's why only those really skilled and experienced should do that. Ask Croatian Mountain Rescue Service if you don't believe, they are probably among the busiest people in Dalmatia during summer, just next to firefighters.
Early autumn, however, is a perfect season for going to Dalmatian mountains, just like early spring. Split offers many options to pursue this urge. Marjan is the most obvious choice, with its many forest paths, but it's more walking than hiking. Still, you'll love it, because it's so easy to walk around, and then even end up on some of its beaches.
Just looking around town reveals two most popular hiking spots near Split, mountains Kozjak and Mosor. On Kozjak (highest peak is 779 meters altitude) there are three mountain homes, in at least one of them (Putalj) it's possible to stay overnight. Route choices are numerous, and all paths are nicely marked with usual hiking marks. To get to the mountain's foot from Split, you can use bus number 37, because it stops in most of possible starting points in Kaštela. There you can choose, whether to go to Malačka saddle, and then walk on the ridge, or go to Putalj, or walk from Klis westbound.
For hiking fans in Split Mosor is even more popular. There is a mountain home there which is among the busiest in Croatia, with good homemade food. Also, it's a starting point to Mosor's peaks, like Vickov stup (1325 meters) or Veliki Kabal (1339 meters). Don't be fooled with not so high peaks, Mosor is a serious mountain you should respect. Here, all paths are also carefully marked, and it's hard to get lost, but don't be reckless. The easiest way to climb is to take bus 28 to Sitno Gornje, and then just follow marked routes.
For those more ambitious, there is also Biokovo, but you need to go to Makarska to start ascend. Same is with Vidova Gora on island Brač, which includes a ferry trip from Split. For now, concentrate on Kozjak and Mosor. For your safety, be cautious, go only if you are equipped with proper clothes and shoes, bring water, charged mobile phone and a map, and don't go alone. Also, do a research, and find out what you can see wherever you are going. For start, all views are spectacular. If needed, call emergency number 112, and then follow Mountain Rescue Service instructions. This is the only way to fully enjoy.
There are many sites which can give you instructions for different routes, this one is good for start, just zoom in map, and choose Split area.