From Sannomiya or Shin-Kobe Station, take the subway to Tanigami Station (10-15 minutes, 4-5 departures per hour). Then, take the Shintetsu Arima-Sanda Line to Arima-guchi and transfer to the Arima Line to Arima Onsen Station (20 minutes, 4 departures per hour). The entire journey takes 30-40 minutes and costs 740 yen from Shin-Kobe and 930 yen from Sannomiya Station.
By direct bus from Kobe
Hankyu and Shinki Bus operate local buses from Sannomiya Station (50 minutes) via Shin-Kobe Station (35 minutes) to Arima Onsen (using bus stop 1 on the map). The one way trip costs 700 yen and buses depart once or twice an hour. Alternatively, JR Bus operates about seven highway buses per day from Shin-Kobe Station (50 minutes) via Sannomiya Station (30 minutes) to Arima Onsen (using bus stop 2 on the map). The one way trip costs 770 yen, while a round trip ticket is available for 1440 yen. The Japan Rail Pass and other JR passes are not valid on any of these buses.
By direct bus from Osaka
Hankyu Bus and JR Bus operate one or two highway buses per hour from Hankyu Umeda Station or JR Osaka Station (60 minutes, 1370 yen) via Shin-Osaka Station (50 minutes, 1230 yen) to Arima Onsen. In Arima, Hankyu Bus uses bus stop 1 on the map, while JR Bus uses bus stop 2. The Japan Rail Pass and other JR passes are not valid on either bus. Online reservations are possible here.
By cablecar and ropeway via Mount Rokko
From Sannomiya Station, take the Hankyu Kobe Line to Rokko Station (7 minutes, 190 yen), from where it is a ten minute, 210 yen bus ride by Kobe City Bus number 16 to the base station of the Rokko Cablecar.
The cablecar ride up the mountain takes ten minutes and costs 590 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 (ten minutes, 260 yen), which brings you down to Arima Onsen (12 minutes, 1010 yen one way, 1820 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 on the cablecar and ropeway plus unlimited use of the circular bus line on Mount Rokko for 1750 yen.
How to get to and around Kobe