Men and women sit around taking in the wood-infused steam, often slapping or brushing themselves with young birch branches, said to aid circulation.
They drink, they snack and they socialize.
Milestones are celebrated here, and moments spent contemplating life too.
Women have been proposed to and many a business deal has been struck between Finnish entrepreneurs.
Revered as a symbol of national pride, nothing says Finland like a Finnish sauna.
This favorite pastime is about one thing and one thing only -- cleansing the body and mind.
Foreigners might find it strange to strip down and sweat in a hot box, but it's just about daily routine for Finns.
Not surprisingly, more than 3.5 million saunas exist across Finland -- a country of just under 5.5 million people.
They build them anywhere and everywhere: from houses and apartments to offices, boats and even the forest.
Heck, even the national parliament has sauna facilities.
And all Finns have their own preferred style of sauna. There are smoke saunas, wood stove saunas, electric saunas and you can rent mobile saunas for personal or corporate events.
There's even an annual event dedicated to mobile saunas in Teuva, western Finland.
But be warned, if you're not Finnish or an old hand at this ancient ritual, there are some things you should know before embarking on a sauna expedition.
Finnish sauna 101
1. Wood works: Finnish saunas are dimly lit and made of pine wood. You won't find colorful lights, fragrant aromas or music.
2. The heat is on: The Finns like their saunas hot, usually up to 100 C. So keeping hydrated and drinking lots of water is crucial. It's not a competition to see who can last the longest -- breaks should be taken to cool down.
3. Keep it clean: You should always take a shower first so you enter the sauna clean. Showering in between or taking a dip in ice-cold water or even snow is all part of the experience. The cold is a shock to warm bodies at first, but is quite exhilarating.
4. Clothing is optional: While Finns don't hesitate to go nude (there are separate areas for men and women in public saunas), there's no obligation to strip down completely. Wearing a swimsuit or covering up with a towel is totally acceptable.
5. Follow the vibe: While most Finnish sauna experiences involve getting naked, there's nothing sexual about it. Any innuendo won't be well received by the locals.
It's about physical and spiritual cleansing and well-being. It's also about bonding and socializing, but it's a place of reflection too -- take in the vibe when you enter and follow that as a social cue.
6. Towels rule: Naked skin should not hit the pine wood of the sauna. Sauna-goers should sit on their towel or use the ones provided in many of the public sauna complexes.
7. Food is fine: Seeing Finns eating and drinking in saunas is normal. This is part of the cultural experience.
8. Steam to taste: There aren't really rules about creating löyly (the steam that comes off the rocks after water hits them). So if you enter a sauna and you'd like it a bit warmer, it's OK to take charge and throw some water on the stove (kiuas).
9. Whipping is normal: A vasta or vihta might be offered. This bunch of birch twigs is traditionally used to gently whip skin, especially over the shoulders. It's said to improve circulation and Finns maintain it enhances the overall experience.
10. It's for everyone: The sauna is for everyone, men, women and children -- although those with serious health conditions should seek medical advice beforehand.
Up until the 1950s, before sauna use became more of a household ritual, the city was full of public saunas.
There are still dozens of them dotted around town, and new public saunas like Löyly and Allas are bringing this age-old tradition to the masses.
Allas Sea Pool
The newest kid on Helsinki's block is the Allas Sea Pool
complex. Opened in September, it sits right in the heart of town by Market Square, and has completely changed the face of the Helsinki harbor area.
It has three pools (fresh water, sea water and one for children) on an enormous floating deck, three saunas (a male, a female and one for private bookings) plus a terrace cafe.
The seawater in the colder months provides for an authentic Helsinki ice-swimming experience. Entry at Allas is around $10 for adults and $6.50 for children.
Swimsuits in the sauna are not allowed but wearing a towel is acceptable. It's open seven days a week.
Allas Sea Pool
, Katajanokanlaituri 2, Helsinki 00160 Finland; +358 40 565 6582
Named after the Finnish word for sauna steam, Löyly
sauna complex opened in May on the Helsinki waterfront, about a 10-minute drive from the city center.
Including its terraces which look out to the Baltic Sea, the building offers saunas, a restaurant and bar serving Finnish food and is a fine example of eco-friendly and contemporary wooden architecture (designed by Joanna Laajisto Creative Studio).
Here, visitors book in for a two-hour sauna session at $20 per person. This gets entry to both the traditional smoke and wood-burning sauna, as well as a towel, seat cover, soap and shampoo.
Access ladders for quick entry to the sea are part of the structure. A third sauna can be booked privately.
Bookings can me made online. Swimsuits are compulsory. Open seven days a week.
Sauna, Hernesaarenranta 4, Helsinki 00150 Finland; +358 (9) 6128 6550
This place is a true Helsinki institution, located in the Kallio district of the city, not far from the center.
Built in 1928, Kotiharjun
's the oldest public sauna in the Finnish capital and other than a renovation in the late 1990s, it's retained much of its original style and architecture.
There are separate wood-burning saunas for men and women, and towels and refreshments are available on site.
Walking through Kallio, it's impossible to miss Kotiharjun -- look for the half-naked men sitting out front with beer in hand and you're in the right place.
Entry is around $11 and towels can be purchased for an additional $2. You can bring your own refreshments, including beer and there's even a refrigerator for them.
No reservations required. Closed Mondays.
Sauna, Harjutorinkatu 1, Helsinki 00500 Finland; +358 (9) 753 1535
Since the 1950s, locals and visitors have been soaking in steam at the Hermanni public sauna
Up to 30 men and 20 women can sauna at the same time in their electric facility.
Visitors can bring their own refreshments or take advantage of the snacks offered, such as traditional herring sandwiches.
The facility recently underwent renovations to give it a cool retro feel. In the warmer months, you can chill out in their garden hammock.
The entrance fee is around $11 for adults. Closed Sundays.
, Haemeentie 63, Helsinki 00550 Finland; +358 (9) 701 2424