Hirauchi Kaichu Onsen (Underwater Hot Spring)

Amazing experience walking down to this onsen at 8pm (low tide was at 10) on a Sunday night, and sharing the place with a few locals. There was an electrical storm on the horizon and the pool was not too hot. Incredible being in warm water while waves rushed in towards us (but never hit us) and watching the lightning on one horizon… and looking up at the stars on the other side of the horizon….unforgettable…

We arrived 2 hours before high tide and just as the rain started. Had the pools to ourselves. There is no attendant. Just put your coins in the money jar. Honour system - at least today. There is a seperate men and womens change hut. We changed into towels wraps and took our kit back to the car. Only two car spots and it is a reverse out location. The two pools are down a concrete path, past the little gates with the change huts left smd right. The pools are in between the rocks down near the ocean. Wear a towel around yourself down the 10m ramp to the pool. Shoes or sandals are left at the end of the ramp above the pools. Drop the bath towel on the edge of the pool and slide in. Caution. The rocks are slipery so go slowly at the edge of the pool and in the pool itself. The two pools are about 1.5. and 2.4m diameter. Keep a modesty towel (a face cloth or small towel) over your lower self if you are really shy, but honestly nobody is looking. You will be sitting shoulder deep in 39 to 41 degree crystal clear water. There is a faint Sulphur aroma but not strong at all. Move around in the rock pool to find cooler areas. Stunning rocks, mountains, forests and ocean vistas are all around so sit back and take it in. As the tide rises the water starts to slop over the edges and cool the pool. Time to take your leasurely leave. We just wore our towels back to the car. Best 300 yen ever.

The onsen is in an amazing location, amidst rocks on the shore line. And it's worth a visit if you're in the area. However, if you're an onsen lover the visit maybe just to say you've been. The bath itself is not very warm and is quite shallow. As you'd expect, it's very popular with both locals and visitors. Despite what I read online, the Japanese ladies in the bath were both wearing bathing dresses. And one of them was definitely local. The Japanese men were naked. There's nowhere to leave your clothes, except on the nearby rocks. If it's windy, weigh them down somehow. I almost my underwear and trousers!

Fascinating unusual onsen. Mixed nude bathing. But you can also have a simple foot bath in one of the the small shallow pools at the end of the walkway. Although the signs refer to lockers, bring a bag to put your clothes in when you go for your onsen and store your gear on the nearby rocks. Take a basin or ladle to wash yourself in sea water near the onsen. With high levels of calcium in the water it is very slippery, so take your time and be careful. As the tide slowly comes in it is fun to move to the small pools closer to the sea and get washed back in.

Very cool place. Highly recommend. The low tide that day was around 2pm; we went around 4:30pm and it was still very good. Almost everyone was local. No one was wearing swim suits, but all the men and women were using towels to cover their bodies. I unfortunately didn’t bring a towel, so I went in fully naked… The people were respectful, but I was worried that I offended them… oh well. Before you go in, grab a little basin and wash yourself with the water from the two smaller pools.

Beautiful rotenburo (outdoor onsen)! Views are great, the temperature of the different pools vary, so you should find one that's just right. Make sure you check the times for low tide and remember this one's a mixed bath and no swimsuits allowed. Women can wear a bathing towel (like a cloth dress), see photo. Honestly, it's a little intimidating being so exposed as the path to the onsen is elevated so people can see you from 50m away and there are a few occupied houses in very close proximity, but if you can get past that, it's great!

Very amused by shoes being left at end of cement walkway instead of the rocks where most people left clothes. Multiple pools but I only tried two of them. Unsure if we're in a low tide time, we stayed nearby for a couple days and anytime we went the water wasn't near. Signs say no bathing suites but most women wore shirts. Public restrooms nearby. At least at this time of year the cliff blocks view of the sunrise.

Very nice natural hot spring. Easily accessible by car. It says everywhere that swimwear is prohibited, but almost all women where wearing it together with a towel. All men bathed naked, but to bring a small towel seems to be the thing to do, to slightly cover yourself when sitting on the side to cool down, or walking around.