By Train
From Sannomiya or Shin-Kobe Station, take the subway to Tanigami Station (10 minutes, 520 yen from Sannomiya; 8 minutes, 350 yen from Shin-Kobe). Then, take the Kobe Railways Arima Line to Arima Onsen Station with one transfer at Arimaguchi Station (15 minutes, 370 yen).
By Bus
Buses to Arima Onsen leave from Osaka Station (60 minutes, 1330 yen one way) and Shin-Osaka Station (50 minutes, 1200 yen) and from Shin-Kobe Station (50 minutes, 750 yen) and Sannomiya Bus Terminal (30 minutes, 750 yen).
By Cablecar and Ropeway via Mount Rokko
From Sannomiya Station, take the Hankyu Kobe Line to Rokko Station (7 minutes, 180 yen), from where it is a 10 minute, 200 yen bus ride by Kobe City Bus number 16 to the base station of the Rokko Cablecar.
The cablecar ride up the mountain takes 10 minutes and costs 570 yen one way or 1000 yen for a round trip ticket. From the top station, take the circular bus line to the top station of the Rokko Arima Ropeway (10 minutes, 250 yen), which brings you down to Arima Onsen (12 minutes, 980 yen one way, 1770 yen round trip).
If you access Arima Onsen via Mount Rokko, you can save some money by using the "Rokko Arima Katamichi Joshaken" ticket, which includes a one way ride of the cablecar and ropeway plus unlimited use of the circular bus line on Mount Rokko for 1700 yen.
How to get to and around Kobe