In the locker room of Sauna Hermanni, one of the few remaining public saunas in Helsinki, I bumped into Paul, an octogenarian who was cooling down after his weekly steam clean, reading his newspaper dressed only in a saggy white vest. I asked him why he came here every week, and after a moment’s contemplation, he said with a shrug: “I couldn’t imagine life without it.”

For Finns, life without sauna is unthinkable, but for it to survive against competing leisure activities and an ever-quickening pace of life, it has had to adapt and diversify.

There was a time when there was a public sauna on every corner of the Finnish capital; they were like the city’s social clubs. Then, during a period of rapid post-war redevelopment, most closed their doors permanently as new apartment blocks incorporated their own saunas and basic washing facilities for residents. By 2010 there were 1.5 million private saunas across the country; about one sauna for every 3.5 people.

Thanks to a combination of renewed civic pride (Helsinki was World Design Capital in 2012), urban regeneration and entrepreneurship there’s now a sense that sauna is being rebranded. Two new public waterside saunas – Löyly and Helsinki Allas – have been designed to not only encourage a younger generation to embrace the traditional and inherently social benefits of public saunas, but also to attract tourists who step off the docking cruise ships looking for something quintessentially Finnish during their brief stay.

These two saunas both boast the sleek, angular lines of Nordic architecture, and are built from ecologically friendly materials. They are prominently positioned on the banks of the Gulf of Finland, sitting proudly as the privately funded flagships of regenerated industrial wastelands. There are bars, there are restaurants. There are even beaches. It’s like a sauna version of London’s South Bank.

These boutique saunas may have added diversity to Helsinki’s sauna scene, but look hard enough and there are still the authentic public saunas dotted around the city that have been keeping the tradition going for decades.

Open since 1953, Sauna Hermanni was – prior to the opening of Löyly and Allas – one of only four public saunas left in Helsinki. It harks back to a golden age of communal saunas and is a shrine to mid-century furniture and decoration, with a 30-berth sauna for men and a 20-berther for women. Sitting in the basement of a nondescript apartment block, I entered the sauna complex and was immediately transported back in time. As I walked through the reception area and into the locker rooms and saunas themselves, I spotted old magazines littered on mid-century coffee tables and pictures of Finnish pin-ups adorning the wood-panelled walls.

Guiding me through the different rooms was the manager, Mika Ahonen, who has been doing his bit to maintain the traditions of the public sauna for four years. A fan of the 1950s aesthetic, he redecorated the place in a vintage style. To help keep punters coming through the doors, he hosts discos with 1970s and 80s music as well as putting on food and drink nights, where he offers sandwiches with sausage (porilainen) or herring, alongside beer. In the summer, there are barbecues. “You can eat, you can drink, and when you come out of the sauna you can talk. It sounds simple, but this aspect is very important,” says Mika.

In search of other public saunas in Helsinki I visited Kulttuurisauna, a sleek, modernist eco-sauna designed in 2013 by Tuomas Toivonen and Nene Tsuboi in the heart of the Merihaka district; and then to the other extreme, the tiny, self-service Sompasauna shacks on the banks of the Gulf Of Finland in the so-called Freezone of Sompasaari (a kind of Mad Max hinterland full of junk yards and disused buildings covered in graffiti). Sompasauna shacks are free to use and maintained by volunteers; visitors may have to chop their own firewood with the saw from blocks of wood provided. Finally I visited the historic Kotiharjun Sauna, the city’s oldest public sauna, built in 1928.

Kotiharjun originally provided the city’s railway workers with a place to wash once or twice a week. Suitably, it produces a furnace-like heat that nears 100C – its steam punk-style stove hissing and spitting heat via metal levers. Once out of the austere sauna, bathers have a shower and sit outside on a little brick wall on the side of the pavement to cool down, drinking and eating. Then it’s back into the sauna for another blast of heat. One sweat-drenched man, who I saw go from the sauna to this quirky little cool-down area five times while I was there, whispered to me as he went back in: “This sauna’s for the hardcore.”

It’s this diversity of public sauna experience in Helsinki that struck me as I drove across the city – depending on your mood you could have a different type of social experience on any given day of the week. But this diversity doesn’t just extend across the capital. There are other sauna options in the north of the country, too.

Two days earlier I had been sitting in one of Lapland’s traditional wooden, smoke saunas, gently broiling in a mellow 70C heat, scents of birch, tar and eucalyptus flaring my nostrils. It couldn’t have been more different from the hustle and bustle of the nation’s capital, and provided another riff on the sauna theme. Instead of cars and trams trundling past, I looked out of the window and saw a frozen lake framed by endless birch trees; their green, early spring foliage contrasting starkly against the luminous whiteness.

Sat next to me was Eveliina Korhonen, a 32-year-old Kenyan-born Finn and sauna tour guide who’s passionate about promoting the health benefits of sauna. Her company provides sanctuary from the noise of modern life via spa-like sauna experiences, including sauna yoga and a visit to a soon-to-be built ice sauna. She had brought me to the Pyhäpiilo sauna near to the winter sports haven of Ruka, 500 miles north-east of Helsinki, and introduced me to a slower, more ritualised process of sauna designed to fully focus on its meditative and health benefits.

To start, she offered me a pre-sauna drink made from tar (terva), honey and water. Extracted from birch wood, tar is considered a panacea in Finland, its properties used to treat everything from skin complaints to digestion and bladder conditions. The Finns like to have it in everything from drinks to soap and as I drank the sweet, slightly acrid concoction, Eveliina recited a Finnish saying: “If sauna, vodka and tar don’t help, the disease will kill you.”

In the sauna itself, there were other treatments. There was a cleansing rub made from Himalayan pink salt, honey and dried birch that I smeared onto my sweaty skin, “whisking” (the gentle flagellation of the skin) with a prickly juniper bush and a dip in the freezing, crystalline waters of the lake outside. All these extras, along with the heat of the sauna, are designed to boost circulation, produce a rush of endorphins and to cleanse and to purify both the body and the mind.

Sauna-goers in Helsinki have to make do with a cold shower or a swim in the Gulf Of Finland, but here, in Lapland, a quick, jolting dip in the frozen lake was all part of the rarefied, quasi-spiritual sauna-spa experience. As I edged my way down the steps, Eveliina bellowed: “Make sure you breathe! Your body will go into shock, so you must keep breathing.” Pleasantly surprised at how refreshing the water was, this effervescence soon gave way to an intense stinging on my legs. It wasn’t very long (30 seconds) until I was almost running back to the warmth of the sauna.

The DJ John Peel was once asked why he loved the band The Fall so much. He answered: “They are always different; they are always the same.” And that’s how I felt about the diversity of sauna experiences on offer. From the fairytale Pyhäpiilo in Lapland to the kitsch Hermanni, intense Kotiharjun and the new boutique saunas in Helsinki, Löyly and Allas, there really is a great choice.

The ancient art of sauna hasn’t changed in 2,000 years – there’s still a stove, there’s still water, there are still benches to sit on and there’s still heat – but what has changed is the variety of places you can do it in. Not only durable, sauna has proved it can adapt with the times, maintain its social, physical and mental benefits while staying at the heart of Finnish culture.
• Sauna prices for adults range from free (donation optional) at Sompasauna to €19 for two hours at Löyly

• This article was amended on 1 July 2016 to clarify a photo caption relating to Sompasuana shacks.