From Austria, via Zagreb and Karlovac to Split; from Italy via Rijeka to Split; from central Italy, by ferry Ancona-Split, then Split-Brač.
There are airports are in Split and Brač, both well connected by bus lines.
In the summer, almost every hour, buses depart from Zagreb to Split, and then you can continue your journey by a ferry or bus. Twice a week from Zagreb the bus goes directly to Bol, with a station in Gornji Humac.
Almost every hour, ferries depart from Split to Supetar, or from Makarska to Sumartin.
It is possible to reach Zagreb or Split by train from all parts of Europe, then take a ferry to Brač, and then continue your trip by bus or taxi.
There are several ferries to Supetar every day and then continue your trip to Bol by bus.