By CHOE SANG-HUN

HOENGSEONG, South Korea - Roasting inside a charcoal kiln has become something of a craze in South Korea. It has its roots in local tradition, much like the sauna in Finland, according to charcoal makers in this mountainous region 90 kilometers east of Seoul. “They come from all round the country to crawl into my kilns,” said Seo Seok-gu, 73, the head of Gangwon Oak Charcoal, South Korea’s largest complex of charcoal kilns. Inside the clay domes, the temperature hovers around 135 degrees

Celsius, so hot that synthetic clothes are banned because they can melt. “We used to sit naked inside the empty kiln at night after a hard day’s work,” said Mr. Seo. “Villagers used to come up the hill, sometimes carrying their sick parents on their backs, to sit in the kilns ,” he said. “Buddhist monks read their scriptures in there .” Both that tradition and charcoalmaking itself declined decades ago, as South Korea industrialized.

But memories of kiln heat baths were revived in recent years by the spread of urban spas called jjimjilbang. Jjimjilbang feature common rooms with heated clay floors where men and women, young and old, relax and sweat. But many also have kiln rooms, which imitate the caldronlike conditions of an actual kiln, even though the heat is mostly generated by electricity.

A decade ago, Mr. Seo said, people began asking for a traditional kiln heat bath. About the same time, charcoal production was enjoying a comeback as urban restaurants turned to charcoal . Mr. Seo charges about $9 per customer for a session. A towel and cotton clothes are provided. For a while, said Seo Jong-won, 37, Mr. Seo’s son and the manager of the complex, “we were making more money from people sitting in our kilns than from selling charcoal.

” There are now about 150 charcoal kiln complexes around South Kore . There are another 150 complexes whose kilns are used exclusively for heat baths, he said. Part of the kilns’ success stems from Korean beliefs in the therapeutic properties of charcoal and clay. Today, homemakers often use pieces of charcoal to absorb smells and purify the air.

In Mr. Seo’s complex, some tourists come to gaze at the glowing charcoal at night, believing this cleanses their minds. “You fight heat with heat,” said Yang Eun-ja, 53, a homemaker from Seoul, explaining why she and other Koreans like to sweat in a kiln on sweltering summer days.

“And in winter, nothing perks you up better than walking out of the kiln into the cold snowy air .” Lim Hyun-o, 40, who used to own an industrial waste treatment factory, said he first visited Mr. Seo’s kilns earlier this year after doctors failed to heal a chronic skin ailment. The condition has now cleared up .

“Some arthritis and cancer patients rent rooms around here and patronize the kilns for months,” he said. “We believe that the heat in the kilns sweats the toxins out of our bodies.” Although some of Mr. Seo’s new competitors boast showers and gardens , his complex has few such amenities. “We haven’t forgotten who we are,” Mr. Seo said. “We’re operating kilns, not a spa.”