Hotel seaside-shimabara [ホテルシーサイド島原] - Discover the Healing Power of Carbonated Onsen- Kicchow

Hotel Seaside Shimabara – Discover the Healing Power of Carbonated Onsen

At Hotel Seaside Shimabara, guests can experience one of Japan’s rarest natural wonders: the carbonated hot spring(tansan-sen). Unlike ordinary hot springs, the water here naturally contains carbon dioxide, creating gentle bubbles that stimulate circulation and are believed to promote relaxation, beauty, and health. Soaking in carbonated onsen water is said to soften the skin, ease fatigue, and even support cardiovascular wellness, making it a truly unique bathing experience.

The bath facilities are designed to let you enjoy both comfort and scenery. The indoor baths provide a calm, modern setting where you can take your time soaking in warm, mineral-rich water. Outside, the open-air baths are surrounded by a Japanese garden, with seasonal greenery and the refreshing sea breeze adding to the sense of tranquility. Guests can also try the round wooden tub for a more intimate soak, or simply relax under the wooden pergola that filters gentle sunlight.

Because carbonated springs are extremely rare in Japan, this is a special chance to try something unforgettable during your trip to Unzen and Shimabara. After a day of exploring hot springs, castles, and volcanic landscapes, bathing in naturally carbonated water feels both refreshing and healing. Whether you visit with family, friends, or on your own, Hotel Seaside Shimabara’s onsen offers an experience that goes beyond simple relaxation—it is an encounter with one of nature’s rare gifts.

My Experience with the Carbonated Spring

What surprised me most was the feeling of tiny bubbles wrapping around my entire body. As I soaked, I could sense the tension in my muscles slowly melting away, leaving me deeply relaxed.

The water stays at about 26°C, which makes it pleasantly cool—an ideal cold spring for the summer months. It felt refreshing, almost like nature’s own sparkling bath.

For me, the best moment was after spending time in the sauna. Stepping into the carbonated spring afterward brought a wave of comfort and refreshment that I had never experienced in any other hot spring before. It was the perfect balance of warmth and coolness, and I left with my body feeling lighter and my mind completely clear.

One of Japan’s Rarest High-Concentration Carbonated Hot Springs

In Japan, a hot spring is officially classified as a carbonated spring when the water contains more than 0.25g of carbon dioxide per liter (250 ppm).
Among them, those with over 1000 ppm are considered high-concentration carbonated springs.

At Hotel Seaside Shimabara, the natural hot spring water contains an astonishing 1800–1900 ppm, ranking among the highest levels in the country.

Bathing in such a rich carbonated onsen is said to have various benefits:

Promoting blood circulation through natural vasodilation
Relieving fatigue and muscle tension
Easing neuralgia and joint pain
Supporting detoxification and overall relaxation

Because of these unique healing effects, high-concentration carbonated springs are attracting attention not only as a rare onsen experience but also as a therapeutic natural treatment.

Soaking in the Onsen While Watching Ships Pass By

One of the highlights of Hotel Seaside Shimabara is the breathtaking view from the open-air baths. As you soak in the natural carbonated hot spring, you can gaze out over the calm waters of the Ariake Sea. The horizon stretches endlessly, and the gentle sound of waves adds to the feeling of deep relaxation.

What makes it even more special is the nearby ferry route connecting Shimabara and Kumamoto. From time to time, a large ship passes by, and you can hear the low, resonant sound of its horn echoing across the water. Sitting in the warm bath, feeling the sea breeze on your face while listening to the ship’s whistle and watching the peaceful scenery—it’s a truly unforgettable moment. For me, it was one of the most unique hot spring experiences I’ve ever had in Japan.

Experiencing the Power of the Indoor Carbonated Bath

When I stepped into the indoor bath at Hotel Seaside Shimabara, I was immediately struck by its unique water quality. This onsen is classified as a Carbonated Bicarbonate Spring (containing magnesium, calcium, and sodium), and its carbon dioxide concentration measures an incredible 1,800–1,900 ppm—one of the highest levels in Japan.

As I soaked, I felt tiny bubbles gently clinging to my skin, almost like receiving a natural massage. The sensation was unlike any other hot spring I had tried before. It is said to be beneficial for neuralgia, muscle and joint pain, bruises, and even chronic digestive issues. For me, the most noticeable effect was how deeply it warmed my body from within, gradually easing away the fatigue of travel.

This type of hot spring is also believed to aid in recovery from cuts and burns, improve circulation, and support conditions like high blood pressure and arteriosclerosis. After bathing, my skin felt noticeably softer, and I even felt that my complexion looked brighter—almost as if the water had revitalized me inside and out.

The indoor bath itself provides a calm and sheltered atmosphere, unaffected by the weather outside. While the open-air baths are perfect for enjoying the sea view and breeze, the indoor bath offers a different kind of comfort—quiet, steady, and deeply restorative. For me, it was a moment to truly pause, breathe, and let the healing power of this rare carbonated spring sink in.

Refreshing Contrast with the Sauna

One of the most enjoyable ways I experienced the onsen at Hotel Seaside Shimabara was by combining it with the sauna. After spending time in the heat, stepping into the carbonated spring at around 26°C felt incredibly refreshing.

The moment I entered the cool water, I could feel the fine bubbles covering my skin, instantly soothing the warmth from the sauna while keeping my body relaxed. It wasn’t a shock like plunging into ice water—instead, it was a gentle and invigorating coolness that felt perfectly balanced.

The combination of sauna and high-concentration carbonated water created a unique rhythm: warming up in the dry heat, cooling down with sparkling bubbles, then resting in calm silence. Each cycle left me lighter, clearer, and more energized than before.

For me, this was the highlight of the stay—an experience that blended relaxation and refreshment in a way I had never felt in any other hot spring.

My Way of Enjoying Hotel seaside Shimabara

At Hotel Seaside Shimabara, every bath offered a unique experience.

I started with the indoor carbonated bath (1,800–1,900 ppm), where fine bubbles clung to my skin and gently eased away fatigue. After the sauna, I cooled down in the 26°C carbonated spring, which felt refreshing and perfectly balanced.

In the evening, the open-air bath overlooking the Ariake Sea was unforgettable. Listening to the sound of passing ships while soaking in the hot spring created a moment of pure peace.

For me, this hotel wasn’t just about bathing—it was about discovering new ways to relax and leaving with memories I’ll carry for a long time.

Why I Recommend This Place

I recommend Hotel Seaside Shimabara because it offers one of the rarest hot spring experiences in Japan: a high-concentration carbonated onsen with 1,800–1,900 ppm of natural carbonation. Few places in the country provide this level of mineral-rich water, and the health benefits—improved circulation, fatigue recovery, and relaxation—are widely recognized.

Beyond the water itself, the hotel provides different ways to enjoy it:

Indoor baths for a calm and restorative soak
Sauna and carbonated spring cycles for refreshment and energy
Open-air baths with views of the Ariake Sea, where you can even hear the horns of passing ships

For travelers coming to Unzen or Shimabara, this hotel combines healing hot springs, seaside scenery, and a unique cultural experience in one stay. It’s not just a place to bathe—it’s a place to recharge your body and create unforgettable memories.