Part of Kagoshima Prefecture, Yakushima lies to the south of the Kyushu mainland. On the southern part of the island is Hirauchi Kaichu Onsen – an onsen which makes its debut at low tide. It is a rare underwater hot spring that is only accessible at certain times of the day.

Underwater onsen

The natural sulphur hot springs that has since become Hirauchi Kaichu Onsen was discovered over 400 years ago. At that time, a visitor noticed that steam was rising from the coast near Hirauchi town. Since then, the residents have taken care of it on a voluntary basis, including creating the bathing pool you can see there now by piling stones and keeping it clean.

Hirauchi Kaichu Onsen is a rarity – it is only available at low tide and bathing is possible for about 2 hours on either side of this time. Otherwise, the waves overtake this area and plunge it in up to 1.5 metres of water. At this time, the comparatively small trickle of hot water mixes with the ocean, making the water very cold; you would never know an onsen lies here except for the signs that are above the water line.

However, the magic happens when the tide receeds. The ocean retreats and the hot water mixes with what remains, creating the perfect onsen surrounded by boulders, rocks and amazing views of both the ocean and the mountains of Yakushima.

My experience

I did this trip with two Japanese friends. We were staying in Miyanoura (in the north) but had a rental car, so were able to go to Hirauchi Kaichu Onsen, which took about 55 minutes to get there. There are two car parks (free, not manned, created by volunteers), so parking is not an issue here. After walking about 100 metres (328 ft), you arrive at the entrance. After paying the ¥300 entrance donation, you go down the boat ramp. There is a white line drawn here, after which no items of clothing should be worn/taken. We left our bags and clothes here, took a face cloth, and went down to the pools.

There are a couple of small ones as well as 2 larger ones. The smaller ones are good for washing yourself before getting in the pools. There are plastic bowls that are supplied for this reason. However, be very careful! The water is extremely hot, so it might be a good idea to mix it with some cold water from the sea first.

Of the two larger pools, the largest sits lower in the water, so it is the first to be swallowed by the encroaching waves when the tide is coming in. The smaller pools, which can comfortably hold about 6 people, has higher walls, so will resist the tide for longer.

When we got there, there were about 6 other people there. Two of them were in one of the smaller pools (a couple from the sound of their conversation and how close they had to be to fit in the pool) and the group of four were in the smaller pool. Our plan was to see the sun set, which was about an hour after low tide. The larger pool had already been reclaimed by the ocean, so we could only enter the smaller of the two. We stayed until this pool was also reclaimed by the ocean.

getting to Hirauchi Kaichu Onsen and info

Hirauchi Kaichu Onsen is here; the best way to go is by rental car. There is also the very rare public bus that stops on Prefectural Route 78. It is best to enquire about the bus information from one of the tourist information centre, such as the one in Anbo, the one in Miyanoura, or the one at the airport.

The time for low tide varies greatly, so you should check when the onsen is available. You can see the times for low tide for Yakushima here. You can use the onsen for about 2 hours on either side of the low tide time listed at the link above.

The onsen is technically free to enter, although they ask for a ¥300 donation to cover upkeep and maintenance costs.

For onsens in Japan, you are usually not allowed to wear clothes. However, as this is an outdoor one that is in the ocean, women may use a towel to cover themselves in the water. Men are naked, although you can use a hand towel to cover yourself when out of the water.

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