The 電気風呂 passes a mild electric current so when you sit between the electrodes, you feel a slight tingly feeling. It’s usually one of the many different types of individual bath options (including jet baths) that a super bathhouse (スーパー銭湯) might have.
They warn people with weak hearts or pacemakers shouldn’t use the devices and I have to heartily (pun intended) agree.
Credit:stackoverflow.com‘