Japan Kusatsu Onsen Guide 2025

Why Kusatsu Onsen Is Japan's Most Famous Hot Spring

In Japan's tradition of onsen (hot spring) ranking — a practice that dates back to the Edo period when samurai and merchants debated which springs had the most therapeutic value — Kusatsu Onsen (草津温泉) in Gunma Prefecture consistently earns the top position. It has been ranked Japan's number one onsen resort in nationwide popularity surveys for over 20 consecutive years.

Kusatsu's ranking is not merely based on reputation — the water quality is objectively exceptional. The combination of high acidity (pH 2.0), high sulfur content, and extraordinary flow rate (the springs produce enough water to fill an Olympic swimming pool every 20 minutes) creates bathing conditions that cannot be replicated by artificial or diluted onsen. The strongly acidic water is said to kill bacteria, soften skin, and improve circulation.

The town has been famous since at least the 12th century, when Minamoto no Yoritomo (founder of the Kamakura shogunate) is said to have bathed here. In the Edo period, Kusatsu became a popular destination for samurai seeking to "wash away" wounds from battle or illness. The famous German physician Erwin von Bälz, who practiced medicine in Japan in the Meiji era, called Kusatsu's waters exceptionally beneficial and helped spread the town's reputation internationally.

The Yubatake: Kusatsu's Iconic Open-Air Hot Spring Field

The Yubatake (湯畑, literally "hot water field") is the visual and spiritual center of Kusatsu Onsen — a large open-air hot spring field at the heart of the town where steaming hot spring water flows from the source into a series of wooden channels and settling pools. It is one of Japan's most iconic onsen images.

The Yubatake was designed in its current form by the architect Isamu Noguchi in the 1960s — the wooden channel system that the water flows through was conceived as a functional design object. The stepped wooden frames that cool the water before it enters the distribution system are both engineering and aesthetic achievement.

The Yumomi Ritual: Paddle-Stirring Kusatsu's Famous Waters

Yumomi (湯もみ) is a traditional practice unique to Kusatsu Onsen — the stirring of freshly drawn hot spring water using long wooden paddles to cool it from its near-boiling source temperature to a comfortable bathing temperature, without diluting the water with cold water (which would diminish the mineral properties).

The yumomi tradition dates to the Edo period when Kusatsu's high-temperature springs were first developed for therapeutic bathing. Because the water was too hot to enter directly, and because the strongly acidic mineral content was considered too valuable to dilute, the paddle-stirring method was developed as a compromise.

The yumomi performance is a living tradition — not a purely tourist recreation. The technique is still used in some of Kusatsu's traditional bathhouses (sotoyu) to condition the water before the bathing pools open each morning.

Kusatsu Water: Acidic Sulfurous Waters — Benefits, Cautions & Skin Types

Kusatsu's water is significantly different from most hot springs in Japan, which are weakly acidic to neutral or alkaline. Understanding Kusatsu's water chemistry helps visitors maximize therapeutic benefit and avoid adverse reactions.

Getting to Kusatsu Onsen from Tokyo: Routes & Transport

Kusatsu Onsen is located in the mountains of Gunma Prefecture, approximately 160km northwest of Tokyo. It is not directly accessible by bullet train — the final leg requires either a highway bus or a combination of train and local bus.