You can see the lake in a calm and quiet environment with relatively few tourists.

Uramashu Observatory is located on the border of Nakashibetsu Town. It is called "Uramashu Observatory" because it is on the opposite side of the first and third observatories in Teshikaga Town. Because the elevation is lower than the observatory on the Teshikaga-cho side, there is less fog and a more mystical view of the lake can be enjoyed. (The seasonal color of the broad-leaved trees along the lakeshore and the dark green coniferous trees, which repeat their seasons, are reflected in the clear blue waters of the lake, and it is simply wonderful.
Overhanging the left side (southeast of the lake) from the observatory is the volcano Mt. Lake Mashu is a caldera lake formed by the sinking of the Mashu volcano, and is surrounded by a sheer caldera wall, which shows the volcanic activity of the lake.
The Mashu volcano, which appeared more than 10,000 years ago at the current location of Lake Mashu, erupted repeatedly, culminating in its largest eruption 7,000 years ago, when it spewed a large amount of ash and pyroclastic flows. The site of the eruption hollowed out greatly, forming a caldera with a diameter of about 7.5 km and a short radius of about 5.5 km. During a period of inactivity of about 3,000 years, the caldera filled with water, giving birth to Lake Mashu, which is larger than it is today. Then Kamuinupuri erupted on the eastern shore of the lake, reducing the area of Lake Mashu by about three-quarters, and about 1,000 years ago, the largest eruption occurred at Kamuinupuri, destroying the summit and giving Lake Mashu its current appearance.
Kamuishu Island, which peeks out from the center of the lake, is a small island, but it too is a lava dome with a surface depth of 211.4 m and a base diameter of approximately 1 km.