The sento is a good place to let your thoughts run. The noises people make as they go about their baths create a sort of calm. At Fukunoyu, in the working class district of Senzoku, I float in the deepest of the three tubs. The view extends down the row of taps and shower heads, to the glass doors of the change room. Some 10 metres above, an arched wooden ceiling caps both the male and female halves of the building. In the afternoon, the sun streams through large windows.

There is something church-like to the sento; perhaps it’s confessional, being naked with others. Then there’s the hard, pristine tiles, the mirrored reflections, the constant murmuring and echoes. The bath is also a womb. Once finished, reborn, you float out as you floated within.

In the deepest tub, which comes up to my waist, the hot water bubbles from below. A large stone placed there emits low-level radiation. It is from the belle epoque Austrian spa of Bad Gastein, and believed to be therapeutic.

It’s only me here, and two older men, who wash side by side on low stools. They’re having a serious discussion, in almost a whisper. They’re probably locals but I start inventing roles for them. A hit man and his client…A property speculator with a secret plan…A private detective extracting information. Showing they have nothing to hide. There’s no chance of eavesdropping, the way the sound bounces around. It would be the safest place to talk.

I pictured the co-manager Hiroto Yamamoto, 25, who is from Fukushima, soaking at another bathhouse around the middle of last year. He told me that’s when he decided he wanted more out of life than his office job. And he liked the sento. He set his mind on running one, and put the idea to his university friend Koudai Takahashi, 23, who is from Saitama. The two made a plan. It shows some initiative. You don’t just acquire a sento, but you can manage one for someone else. Although there is no manual for how to do this.

Takahashi says he began phoning bathhouses to see if they wanted someone to take over. “I called about 150 places in the end,” he says, leaning back on the leatherette sofa in the foyer with its fake fireplace and view over a small garden. “Some of them got angry. Are you messing with us?”

And this is where they ended up, earlier this year, two out-of-towners in an unfamiliar, rough-edged neighbourhood near the Yoshiwara soaplands. Yamamoto says the Fukunoyu owner, a third-generation bath operator, “just wanted to do something else.”

The locals have taken to them, chatting easily on their way in or out, stopping for a drink in the foyer or at a table in the change rooms. In the busiest week this year, over 800 customers came. The bathmen have a community around them: at a recently opened vegan cafe across the street and, nearby in Iriya, friends who have remodelled a former sento into a timber-walled cafe and remote-work space. The two teams promote each other: coffee and bath coupons — and even coffee grounds baths. Yamamoto and Takahashi work with other local ventures, like yoga at a temple followed by the bath, or a day for kids when they turn the foyer into an old-style dagashiya sweets shop. They have installed a draft beer server and as members of the Tokyo sento association, receive infusion bags of lavender, or yuzu citrus in winter, to float in the water on official “Sento Day”. They also plan to make baths with the lees from sake, brewed rice.

Fukunoyu surprised me when I stumbled upon it, as I had passed it before and not noticed. There is no big sign. On that day there was a young woman at the counter. The next time I went she had gone. The men say they put out calls for partners on Twitter; their members went from two to four, to three and then back to the original two. In the end their ideas for the place were all different, and Takahashi and Yamamoto do all the work themselves. Takahashi even sleeps there when it’s too late to go home.

The hollow echo of plastic basins hitting the tiles, washcloths slapping, the clunk of the push-taps, water flooding, the bubbling tubs. All the sounds are familiar and predictable. That’s what makes the place meditative. Unusually for a sento, Fukunoyu also plays background music, a quiet jazz piano, like someone thinking aloud. The notes waft above the dim roar of the furnace, which burns behind the large mosaic of twisted pines on a coast.

Fukunoyu, 2-34-6 Senzoku, Taito-ku Tokyo tel. 03-3872-7089. No closing day

The bathmen: Koudai Takahashi (left), Hiroto Yamamoto