We had not seen each other since we graduated from the same exurban New Jersey high school, and we lay in our spa-issued cotton uniforms, toggling between gossip about our old classmates and Arcadia’s explanation of Korean spa and beauty practices. The details she provided from her own life were intriguing. Her 4-year-old daughter and some of her friends had perms. When her family took a portrait together, the photographer had used Photoshop to slim Arcadia’s arms without asking first. For a few weeks after her third child was born, she had checked into one of Seoul’s newly popular postnatal spa-hotels, which offers daily massages, lactation help, 24-hour infant care and luxurious, quiet rooms.

But Arcadia, the most confident person I knew in high school, had never been to a jimjilbang before, in part because even she had been intimidated by the prospect of silent judgment. “This is where mothers take their daughters-in-law to check out the marital packages,” she said, only half-joking.

Last year on a family trip to Japan, my husband, daughter and I visited Hoshinoya Karuizawa, a resort in the mountains northwest of Tokyo that turns bathing into an experience of minimalist splendor. We soaked for hours each day, moving silently through pools devoted to meditation, immersing ourselves in wooden baths filled with kumquats, and watching Japanese families relax in outdoor pools that mimicked mountain streams. The Hoshino chain, with its contemporary versions of traditional Japanese ryokans, or inns, is an example of Japan’s genius for preserving its culture while marketing it to outsiders — a skill that Korea, for all of its energy and success, still largely lacks. In Tokyo, we also visited more modest bathhouses, neighborhood joints with vending machines and large-screen TVs in the lobbies. But even those places carried a glow of cleanliness and serenity: the bath as Shinto-Buddhist ritual.

Korean jimjilbangs are their cousins, newer versions of the public bathhouses that became popular during Japanese rule, and some of the facilities look the same in the two countries, down to the little stations where you rinse yourself before immersing in hot medicinal pools. But going to a jimjilbang in South Korea can be like having a shvitz and a bath at a mall — in some cases, a mall that is on a cruise ship. The most elaborate jimjilbangs are multistory, self-contained universes with magic shows, Korean barbecue restaurants and corporate team retreats. (According to one Korean expression, you’re not really friends with someone until you’ve bathed together naked in a jimjilbang.) A popular TV variety show even has a regular segment set in a jimjilbang called, “Don’t Laugh in the Sauna.” The host asks celebrity guests nosy questions in a funny accent, and if they laugh, they are doused with water.