Mount Asama dominates the park's southwest quadrant, rising 2,568 meters above sea level on the border of Gunma and Nagano prefectures. It is the most active volcano on Honshu, with a historical eruption record stretching back more than 1,300 years. Since 1108 AD, Asama has erupted at least 118 times, averaging one eruption roughly every eight years. Its 1783 eruption killed 1,400 people and ranks among the most devastating volcanic events in Japanese history. Even in quieter periods, wisps of sulfurous gas rise from the summit crater, a persistent reminder that the mountain is merely resting. Nearby, Mount Kusatsu-Shirane reaches 2,160 meters and guards a cluster of crater lakes around its summit, including Lake Yugama, a cobalt-green pool with a diameter of 300 meters and waters so acidic almost nothing can survive in them.

The Shiga-Kusatsu-Kogen Ridge Highway is the park's scenic spine, an alpine road open from May through mid-November that threads between volcanic peaks and through highland meadows. The route connects two very different worlds: to the south lies Karuizawa, a refined resort town reachable from Tokyo by the Nagano Shinkansen, and to the north the Yamanouchi hot springs, including the steaming onsens of Yudanaka. The highway climbs past Mount Shirane and Mount Yokote, offering views across a landscape where volcanic steam vents punctuate alpine grasslands. Driving it feels like crossing a geological timeline, from the forested valleys below to the bare, mineral-stained rock of the high volcanic zone.

When winter buries the plateau under meters of snow, the park transforms into one of Japan's premier skiing destinations. Shiga Kogen, Japan's largest ski resort, sprawls across the eastern portion of the park with interconnected slopes that hosted events during the 1998 Nagano Winter Olympics. Sugadaira offers additional terrain nearby. The same volcanic geology that produces the park's hot springs also creates ideal conditions for onsen-side apres-ski, a combination that has made this region a magnet for winter visitors. The heavy snowfall here is legendary, driven by cold air masses sweeping across the Sea of Japan and colliding with the mountain barrier.

Joshin'etsu-kogen National Park was significantly expanded in 1956 to absorb the Myoko-Togakushi mountainous region to the north. For decades, these two areas existed under a single administrative umbrella, but their distinct geographic characters eventually led to separation. On March 27, 2015, the northern section was designated as its own entity: Myoko-Togakushi Renzan National Park. The split left Joshin'etsu-kogen as a tighter, more volcanically focused park, centered on the Asama-Shirane volcanic corridor and the highland plateaus between them. It remains one of Japan's most geologically active national parks, a place where the earth's interior is never far from the surface.