Deep underground in a disused iron mine and under the bluish glow of a flashlight, a small crowd emerges from a sauna, steam rising off their bodies as they plunge into a crystal clear turquoise lake.

In Sweden and Finland, some unusual saunas have been built in recent years, offering truly singular experiences.

Nestled in the snowy forests of Bergslagen in central Sweden, hidden 90 metres (almost 300 feet) below ground in this region known for its mines, lies this very special sauna.

The old iron mine in the town of Borlange closed in 1968 before reopening in 2022, redesigned to welcome visitors looking for a unique -- and sweaty -- experience, Daniel Karlsson, the head of Adventure Mine, told AFP.

"If you look at saunas today, it's more like a luxury experience," he said.

But "down here it's not just a sauna. It's also the experience that you get with nature," he said, clad in a thick red parka to protect from the cold and a helmet with a headlamp.

The space offers visitors a moment of respite from the busy, connected world above.

"Because the sauna is down in the mine, there is nothing that disturbs you from enjoying the sauna."

"You don't have mobile phones, you don't have the sun, you don't have the wind," he said.

- Heat on a high -

 

Saunas are enjoyed around the world as a method of relaxation, claimed by some to provide health benefits.

They originated in Finland and Estonia, typically built as small wooden cabins where dry heat up to 100 degrees Celsius (212 F) with very low humidity is produced from a stove or hot rocks.

Having a sauna has been a social and hygiene tradition for more than 2,000 years.

Now, sauna enthusiasts who want to expand their horizons can reach new heights in Helsinki.

In the Finnish capital, a giant ferris wheel overlooking the city offers a sauna in one of its specially-built pods.

The sweat session could easily burn a hole in your wallet though, costing between 240 and 350 euros ($255 to $375).

"You can get a pretty good steam and heat here if you really want to," said shift manager Viivi Makelainen.

"Although it's pretty small, you can fit quite a few people in here, four or five. Also the views are more fun when you're in the sauna."

Saunas are an integral part of daily life for most Finns.

The country of 5.5 million inhabitants is home to 3.3 million saunas.

Traditionally considered a sacred space in Finland, 'a church of nature', the Finnish sauna culture was named a UNESCO Intangible Cultural Heritage of Humanity in 2020.

 

- 'Intimacy with the surroundings' -

 

Saunas in the Nordic countries are typically small wooden cabins located near the shore (for a quick dip), deep in the forest (for a quick roll in the snow) or in a home (with a quick shower to refresh).

But one special sauna in the Stockholm archipelago is making waves -- sailing on the waters of the capital city.

The "Big Branzino", a luxury floating sauna measuring 30 square metres (322 square feet), was designed and built in 2022 at the request of a private person.

The structure resembles a square wooden cabin, featuring floor-to-ceiling glass windows and an open-air wheelhouse on the deck.

Inside, a custom-made wood stove with hot rocks is surrounded by wooden benches and chairs, while outside, a rooftop terrace features a large table and seating area to take in the view.

"A client came to the firm and he wanted a truly extraordinary sauna that he hadn't seen before," architect Johan Strandlund told AFP.

"So we came up with this shape in order to really maximise the intimacy with its surroundings, and we also wanted a truly breathtaking presence on the horizon," he said.

Strandlund said the floating sauna appealed to nature- and sauna-loving Swedes.

"I think it's the way that we really like to enjoy the beautiful nature that we have around here in Stockholm."

And "even when you're not using the sauna, the fire is a great source of heat, for example for cold summer nights."