The best ways to get to Okutsu Onsen Hostel.
Address: 63 Okutsu, Kagamino, Tomata-gun, Okayama 708-0503, Japan
Mobile or WhatsApp +81 809 800 4810
Co-ordinates: 35.224148 and 133.919868
From Osaka:
There are 2 direct buses from Osaka to Okutsu. (¥3,700) It is the Nihon Kotsu Express Bus from Osaka to Misasa.
The first one leaves from Namba OCAT (Osaka City Air Terminal next to JR Namba station) at 10:30 and arrives in Okutsu 13:18. The second bus leaves from Shin-Osaka station at 17:70 and arrives in Okutsu at 20:53. The bus stop in Okutsu is opposite the Okutsu roadside station. To walk to the hostel, walk onto the parking lot of the roadside station and look for the toilets. Behind the toilets there are stairs leading down to the city center, before the bridge take the road on the right parallel to the river. Just past the grocery shop you will see the sign to the hostel. Look here on google maps!
Here is the bus timetable (pdf)
From Tsuyama:
From Tsuyama there are 9 bus connections per day. 
There are 4 direct buses from Tsuyama station to Okutsu. There are 5 bus connections with 1 change of bus. The strange situation exists that the direct bus cost ¥980 and when you travel with the one connection it only cost you ¥400 (you have to pay twice ¥200) You have to change bus at Plant5 which is a large shopping center. (see timetable above) The ladies of the information center at Tsuyama Station are very helpful and can provide you with the timetable. There is also a community bus which travels around Tsuyama and Plant5 which costs ¥200.
From Tokyo:
Depending on your time frame and budget. There is a night-bus from Tokyo Shinjuku to Tsuyama which cost ¥10,000. An other solution is to take the Kintetsu Express bus from Tokyo to Osaka (¥4,000) or travel by train/shinkansen to Osaka and from there take the bus.
From Okayama:
From Okayama the best way is to take a train to Tsuyama station (¥1,100), just 90 minutes and travel to Okutsu by bus. (¥400). There are hourly trains between Okayama and Tsuyama.
From Tottori airport:
From Tottori airport there is an hourly train connection that takes you in 53 minutes to Kurayoshi train station.( ¥ 590) Check timetable here. From here walk to the Kurayoshi Bus Center. There you find twice daily a bus to Okutsu, which stops at the road side station in Okutsu.
Here is the bus timetable (pdf)