Taiji Hamano slips into the scalding hot water of Kimurayu bathhouse without a moment's hesitation. In seconds the 91-year-old is immersed from the neck down, his head framed by a flaking, handpainted mural of Mount Fuji.
For Hamano, a soak in the company of a handful of other men is a daily ritual stretching back decades.
"We had a bathtub at home even when I was a boy but I much prefer coming here," he says. "The bath is nice and big so you can stretch out and take your time. It's a form of stress relief."
But Hamano, who lives a few blocks away in a tranquil corner of Tokyo's Nihonbashi district, is fast becoming a rarity.
In their heyday in the late 1960s there were almost 18,000 public bathhouses, or sento, in Japan, and almost 2,700 in Tokyo alone.
Nationwide the figure has slumped to just over 5,000 and in the capital, weekly closures over the past 30 years have taken the total below 1,000.
The bathhouse culture fell victim to Japan's postwar economic success, which by the 1960s had given working-class Tokyoites the means to buy new homes complete with their own baths and showers.
The rise of the stay-at-home bather has left many sento owners pessimistic about their long-term future.
"We used to get more than 400 people a day, but now we're lucky if we get 100," says Nobutoshi Yoshida, owner of Kimura-yu, a ramshackle bathhouse that has changed little since it was built in 1930.
Rising costs and faltering attempts to improve bathhouses' staid image threaten to bring to an end the Japanese ritual, stretching back 800 years, of relaxing in a tub of frighteningly hot water in the company of one's neighbors.
In the postwar era a trip to the sento doubled up as a chance to catch up on the neighborhood gossip; these days, however, "bathing out" is more likely to involve a trip to one of the super-sento that have sprouted up in big cities.
One of the most popular is Oedo Onsen Monogatari in Tokyo's Odaiba district, a ?5 billion (US$43.5 million) collection of baths that recreate the atmosphere of 19th century Japan. Well over 4,500 people a day visit Oedo at weekends, many of them families who spend an entire day testing waters pumped from 1,400m below ground.
"The traditional sento were a part of daily life, but the super-sento are for younger people and families who look on them as theme parks," says Shinobu Machida, Japan's foremost expert on sento and the author of six books on the subject.
"The social side of going to a sento simply doesn't appeal to younger Japanese," he said.
Tokyo's sento association, which oversees all of the city's bathhouses, has recently banned smoking in an attempt to attract younger bathers, for whom the traditional sento conjures unsavory images of middle-aged men, wearing only a strategically placed hand towel, puffing on a cigarette as they cool off in the changing area.
But even a sento fanatic like Machida admits that the Japanese tradition of hadaka no tsukiai (naked friendship) is on its way out.
"Only old people seem to go to their neighborhood sento these days," he said.
But Yoshida appears resigned to his fate.
"It wouldn't come as much of a surprise if we closed down tomorrow," he said. "On the other hand, regular bathing is part of what it means to be Japanese, so I haven't given up hope yet."