Kinosaki Onsen is located close to Kyoto, Osaka, Kobe and Himeji, making it easily accessible by train and bus. It is also located along JR lines, meaning that JR Pass, JR West Pass and Kansai Wide Area Pass holders can use their passes to reach Kinosaki Onsen.
There are express trains between Kyoto and Osaka to Kinosaki almost every hour. Although most trains are direct, some will require a quick transfer in Fukuchiyama. There are also express trains from Himeji and Kobe. Access from Kobe takes roughly 2h 40 min. From Himeji it takes roughly 1h 50 min.
There are two round trip flights from Osaka Int. Airport and Tajima airport per day. The flight duration is around 40 min. From Tokyo, you can fly from Haneda to Tajima airport with a transfer at Osaka Int. airport. The whole journey from Haneda to Tajima takes about 2h 10 min. Taxis from Tajima airport to Kinosaki Onsen take about 30-40 min.