Joshin'etsukogen National Park ( Jōshin'etsu Kōgen Kokuritsu Kōen) is in the Chubu region of Japan; it is the second largest national park in Japan and consists of mountains and highlands that extend across Gunma, Nagano, and Niigata prefectures.
The nearest town of size is Nagano, easily reached by Shinkansen from Tokyo (79 min). From Nagano Station, the Nagaden Shiga Kogen express bus runs several times a day directly to Shiga Kogen (1 hr 10 min, ¥1600). All buses go up to Hasuike (蓮池), with some continuing on to Oku-Shiga Kogen (奥滋賀高原) or Shirone Kazan (白根火山).
Alternatively, if you miss the direct bus, take the Nagano Dentetsu train from Nagano to Yudanaka (40 min) and continue by bus to Shiga Kogen (20 min, roughly hourly).
On your journey, you might see some of these notable mountain locations: Mt. Asama, Mt. Shirane, Ichinokurasawa, Shibu Pass, Mt. Myoko, Mt. Kurohime, Mt. Togakushi, Mt. Iizuna, or Lake Nojiri.