If you are coming from Tōkyō, first head to the Kōriyama station in Fukushima prefecture. It is possible to get there in about 80 minutes with the Tohoku Shinkansen.
※ There are also shinkansen that do not stop at Kōriyama, so please check when taking the train.
From Kōriyama it is necessary to proceed using the traditional railway line. With the Ban’etsu West Line headed to Aizu-Wakamatsu station you can arrive at Inawashiro station in about 40′. If you take the Aizu Liner rapid train (no overcharge needed), you save even more time. The one way cost from Tokyo is 8500 yen, including the Shinkansen fare, and totally covered by the Japan Rail Pass.
From the bus stop in front of Inawashiro station there in more or less one bus leaving every hour. From the station the Bandai Tōtō bus takes 35′ to the Goshiki-numa entrance.
(for more information follow this link Toto Bus Timetable (in Japanese only))
For those who want to travel cheaply or prefer travelling during the night, from Tokyo to Kōriyama there are also intercity buses. Depending on the period, there are also buses that go to Inawashiro station.
(for information about seat availability, fares, etc. please follow this linkhttp://tinyurl.com/ms22lzn)