A SENTO where has the blackest ONSEN in Tokyo – KAISEIYU, Tokyo

Tokyo is famous for KUROYU (black ONSEN).


Many of ONSEN springing out in Tokyo is KUROYU which is ONSEN colored black, and here KAISEIYU has the blackest ONSEN just as coffee.



KAISEIYU is located at KAMATA, OTA Ward in Tokyo. Although it’s SENTO, it provides natural ONSEN.

It’s sodium – hydrogen carbonate cold mineral spring, and it also has spring source.


Look at this color!!



In addition to its color, they also have Carbonate black ONSEN which you can only experience at KAISEIYU in Tokyo.

It’s just like you are bathing in cola.


Moreover, they have started to have highly concentrated carbonated spring + hydrogen spring which is also the first place you can experience in Tokyo.


One of the features of KAISEIYU is that a lot of carps and sharks are swimming at glass tank.


There are some SENTO where has glass tank with goldfish, but here a big glass tank is on the wall and uncountable number of carps are there. Surprisingly there are sharks also.


Look at this large crowd of carps and big size glass tank!!




The recommended way of bathing here is to enjoy the view of fish swimming with also enjoying bathing in highly concentrated carbonate spring. As carbonate spring contains carbonate micro bubble inside, it’s advisable to bathe very calmly. That is because the carbonate goes flat if you move or splash too much, just as cola goes flat if you shake it too much.


In addition, carbonate spring has an effect to make your blood circulation smoother because your body reacts with carbonate and regard it as foreign material and start circulating more blood. Therefore, by bathing in carbonate spring calmly, you can detox with widening your blood vessel and get your metabolism better.


It also gives you a kind of mental detox by watching carps swimming slowly and bathe in ONSEN comfortably.


Another feature of KAISEIYU is its wonderful rooftop.


KAISEIYU has wonderful rooftop though it’s not usually open to public except when some special events are held.




A huge icon of SENTO and logo of KAISEIYU which should be visible from the sky.

It also has a big black chimney which even Santa Clause might be able to enter from here.

I wish someday the owner permits us to drink beer here!!


The owner of KAISEIYU is the fourth-generation owner.


KAISEIYU started operation in 1929. It has been run by family and the current owner is the fourth-generation owner.

As you can see from its interior and exterior, it has been renovated and re-arranged to a modern way.


Modern exterior and relaxed interior.




Below pictures are a kind of wordplay expressing “Open” or “Closed”.

1st picture shows “WA” in HIRAGANA character in Japanese on the wooden board which means “ITA” in Japanese, which is to say “WAITA” in Japanese means ”Bath is ready” thus meaning “It’s open”. On the other hand, the 2nd picture shows “NU” in HIRAGANA character in Japanese on the wooden board ITA, which is to say “NUITA” in Japanese means “Bath has been closed”.




During the Edo period, such wordplay was one of the trends people loved.


Not just keeping the old Japanese culture, KAISEIYU is challenging various new things.

One example is that they float hundreds of rubber duck on the bathtub for customer to enjoy.

Another example is that they are selling “KUROYU Cider” which is locally developed beverage in this Ota Ward.

Why don’t you drink KUROYU Cider after bathing in carbonate spring? It makes you really fizzy and bubbly.





In addition, KAISEIYU often holds SENTO YOGA and SENTO RAKUGO (Japanese comic storytelling).




This good old SENTO has been kept running with challenging spirit to fit the modern days.


*Photos are taken with permission when a special event was held. It’s not usually permitted to take photos.


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