Had I ever seen so much bare flesh in one room? Naked in a mixed-gender Austrian sauna, I sat opposite two dozen other nude people on wooden benches. Even after more than a year of living in Europe, as an American, I still felt a little uncomfortable sitting there in nothing but my own skin.

The sauna master came in to warm things up. Tall and lanky, wearing just a towel wrapped around his hips, he wheeled in a cart with several grapefruit-size balls of crushed ice infused with essential oils such as black pepper, lime and eucalyptus. After a short speech telling us to leave immediately if we felt dizzy, he placed one of the ice balls onto a tray of hot coals, and it began to sizzle. The smell reminded me of an expensive aromatic candle: a touch sweet, a touch spicy.

He twisted forward, backward and sideways with a large towel clutched between his hands, like a half-dressed matador, moving the air around the room with a singular goal: to get us very, very hot, as part of a sauna ritual called aufguss, German for “infusion.” As I watched, mesmerized, I began to forget my awkwardness — or that I was even naked.

No swimsuits allowed

Austria and Germany abound with spas called thermen — resorts with pools, saunas, lakes, restaurants, bars and treatment areas. Typically, they have a warm mineral spring, and a section where nudity is required. Walk in wearing swim trunks and you’ll get glares and maybe even reprimands.

I had traveled to St. Martins Therme & Lodge in Frauenkirchen, a small town about an hour southeast of Vienna. St. Martins stands next to a serene, shallow lake where guests can swim in the summer or take a cold plunge in winter. At the center of the therme is an atrium with a pool that has indoor and outdoor areas connected via a tunnel, floor-to-ceiling windows that look out onto the lake and several levels of balconies with rows of lounge chairs. The complex has five saunas and a steam room; 11 thermal pools; a treatment area with massages, facials and more; a restaurant; and a cafe. A day pass is 53 euros (about $58).

After about five minutes of intense sweating in the sauna, we moved on to the second stage of the aufguss: Still naked, we filed outside into a courtyard with a whirlpool and walls covered in vines. My skin was so hot that the normally stinging 40-degree November air felt like a balm. An attendant handed each of us scoops of a salt-and-coconut-oil scrub, which we dutifully rubbed into our skin.

Thoroughly scoured, we returned to our perches inside, where the sauna master whipped out an oversize fan and spent the next six or seven minutes in a hot-air crescendo. After about 15 minutes total, the aufguss ended, and we flooded back out through the door, our bodies bright red and steamy.

Sit back, relax and ‘don’t stare’

The aufguss is just one of the joys of a day at a therme, which might also include a body treatment, a soak in a heated outdoor pool with rotating jets and a fresh schnitzel with an icy glass of wheat beer or sparkling apple juice. For locals in German-­speaking countries, the aufguss is a hugely popular pastime, especially in the late fall and winter.

“I really enjoy it after a week of hard work, or when I just need relaxation, or if my body is really tense and my muscles are really stiff,” said Laura Blumenstiel, 29, a psychologist from Freiburg, in the southwestern corner of Germany, who has been a frequent visitor to thermen for about decade.

Typically, a therme complex is divided into two sections: one with several heated indoor and outdoor pools, where bathing suits are required and children are allowed, and a second that usually contains all the saunas, where clothing is verboten.

For some Americans, including me, nudity, especially in a mixed-gender environment, can initially feel extremely uncomfortable. Keon West, a professor of social psychology at Goldsmiths, University of London, explained that cultural standards often affect what level of nudity people find tolerable: In some places, seeing women with their hair uncovered might feel racy, while in others, stripping down on a public beach is perfectly acceptable.

In countries like the United States, he said, there is a “highly sexualized and puritanical culture, where sex is tightly controlled. Attitudes are generally much more conservative concerning what women do and women’s bodies. In Europe, that tends to be less of the case.”

In a number of studies, West and his team have found that being naked around others can increase self-confidence and life satisfaction. “If you go to a naturist event, you see a lot of normal people, people who aren’t airbrushed and aren’t Beyonce, and you realize you don’t look bad compared to the average person,” West said. “And you spend time naked in their company and nothing bad happens. No one says anything bad to you, no one laughs at you.”

Some Americans have found that the discomfort of being nude in the sauna is fleeting and has a worthwhile payoff.

After moving to Graz, Austria, Amy Feineman, 38, a saddle fitter originally from Colorado, made the hourlong drive to Rogner Bad Blumau, a colorful, trippy therme and hotel designed by Friedensreich Hundertwasser, an Austrian architect who believed that “the straight line is the curse of our civilization.” At the therme (day visit, 57 euros), this philosophy translates to wavy floors and circular buildings with uneven ceilings. On their first visit, Feineman and her husband skipped the nude sauna area, instead exploring the pools and outdoor gardens partly clothed. But on their second visit, they felt brave enough to bare it all in the sauna area.

“It took us most of our first day there to build up the courage to check it out, and then we spent most of our time there,” Feineman said. “I’m a plus-size person, and in the U.S., I would never wear a bikini in public. Here, I’m happily walking around the nude area.”

Feineman and her husband are now regular guests at Rogner Bad Blumau. Her main piece of advice for other nervous Americans? “Don’t stare,” she said. “And don’t worry about them judging you either.”

Sweltering soundtrack

The sauna master was playing pulsing Austrian pop music and handing out bottles of cold, nonalcoholic beer to the 40 or so of us gathered at Alpentherme Gastein, about 90 minutes south of Salzburg (day visit, 45.50 euros), for a party-­themed evening aufguss. The balls of crushed ice flashed from the lights shining beneath them, and he encouraged us to chat, a rarity in most saunas.

Aufguss sessions come in all different types. Some sauna masters blast Metallica, while others prefer calming beats. Some dress up as Vikings. But there are two immutable rules: No clothes, and don’t enter an aufguss once it’s started (you can leave anytime).

A few other tips: Always sit on a towel in the dry saunas, claim your spot at an aufguss a few minutes early (the higher you sit, the hotter you’ll be), don’t bring your phone into nude areas, and shower before entering.

I had come a long way toward embracing my naked self by the time I sat down in the party-themed aufguss and started grooving to the music. It required a little bit of letting go: of my fears, of my ego and of my control. Glancing around — without staring, of course — I could see that no one around me looked like Jennifer Lopez or Jeremy Allen White. We were all just beautiful lumps and bumps.

Was anyone judging my body? To be honest, I was way too hot to care.