AMNA NAWAZ: Well, the sauna industry in the U.S.

is heating up.

More and more health-conscious Americans are embracing this ancient Finnish tradition as a modern way to help reduce stress and promote wellness.

GEOFF BENNETT: The surge in popularity is happening nationwide, but nowhere has the sauna culture taken root more deeply than in Minnesota.

Kaomi Lee from Twin Cities PBS has the story.

KATIE USEM, Owner, Sisu + Loyly: These are front-row seats, so it's about as close as you can get to Lake Superior and enjoy it from the inside of a sauna.

KAOMI LEE: This sweeping view is from one of two cedar-lined saunas at Sisu + Loyly in Grand Marais, Minnesota.

Owner Katie Usem explains the name sisu comes from Finnish, a nod to the Nordic-style sauna experience she's brought to life here.

KATIE USEM: It refers to the concept of fortitude, tenacity or grit and loyly refers to the steam that rises off of the sauna rocks when you put water on them.

KAOMI LEE: Her dream to start a business on the shores of Lake Superior began when she and her family moved here after COVID.

That's when Usem stumbled onto this lakeside property, which included an old fish house.

It was in need of a lot of repair, but it sparked an idea.

She and her husband invested a million dollars between savings and loans.

At first, some wondered if their business was just hot air.

KATIE USEM: I know there were some people when we opened up and started talking about creating a sauna business, some people were like, how are you going to make money at that or will that last?

KAOMI LEE: The risk paid off.

Four years later, Usem now has eight part-time staff.

A floating sauna and a mobile sauna have been added and there's more to come.

About 100 miles south in the city of Duluth, Justin Juntunen has had the same success.

He believes saunas, pronounced sauna in Finnish, are having a moment and he expects it to last.

JUSTIN JUNTUNEN, Co-Founder, Cedar & Stone Nordic Sauna: We're too stressed out.

We're full of anxiety.

We're post-COVID.

We're post this pandemic and we're looking for moments to be real humans next to each other, and sauna does that.

KAOMI LEE: Justin is a sixth-generation Finnish American.

His business features two wood-fired saunas and a cold plunge in the lake.

In warmer months, he opens a floating sauna like Katie Usem's.

He also designs and builds saunas, shipping out 10 a month all over the country.

He now has 70 employees.

JUSTIN JUNTUNEN: We're about a $5 million dollar company today for top-line revenue every single year.

We have just expanded our manufacturing so that we can do more.

We have had over a yearlong wait list for our saunas for the last two years.

KAOMI LEE: Juntunen says Minnesota is one of the epicenters of the sauna boom in the U.S.

This makes sense considering Finnish immigrants first arrived here in 1864 and brought sauna culture with them.

He says investors across the country and abroad are also getting in on the trend.

JUSTIN JUNTUNEN: Today, we're seeing a lot of investment into the sector broadly, big, big companies, big European companies wanting to come into the States, other homebuilding sort of infrastructure companies buying sauna companies.

KAOMI LEE: Glenn Auerbach isn't surprised.

He's been a sauna evangelist since the 1990s.

GLENN AUERBACH, Author, Saunatimes: I call it the holy trinity of good sauna, and it's heat, steam and ventilation.

It's really that simple.

KAOMI LEE: He was an early champion of the mobile sauna movement in the U.S.

A decade ago, he built one of the first portable saunas in the country.

After all his time around saunas, he told us they can have an impact on overall wellness, improving sleep or helping with pain from arthritis, among other things.

But he says you should take all specific claims with a grain of salt.

GLENN AUERBACH: If one is leading with health benefits, I think that it's a tail wag in the dog.

I mean, enjoy it and then health benefits down the road.

KAOMI LEE: For Katie Usem, taking her clients down that road begins with a calm space to unplug and restore.

Hot tea, fluffy bathrobes and salt scrubs are all part of the experience.

KATIE USEM: It's not just a transaction.

Whether it's making their lives better or they just happen to just really enjoy the 90 minutes that they spent here or the two hours they spent here, you see it.

KAOMI LEE: More and more Americans are seeing it too, as the popularity of this centuries-old Finnish tradition continues to heat up.

For the "PBS News Hour," I'm Kaomi Lee in Grand Marais, Minnesota.