How Adventuremine Built a Sauna 280 Feet Below Sweden

Adventuremine’s sauna windows needed a 12-person crew to reach their destination. Six people carried at a time, then traded places on the route from the surface into a former iron-ore mine in Tuna Hästberg, Sweden. The glass had to survive the same rugged underground passage that future guests would walk to reach the heat.

The sauna opened in October 2022 beside an underground lake. In an October 15 interview by email with SaunaNews, founder and CEO Daniel Karlsson described how he and Stefan Olsson designed and built it, from timber taken from their own forest to a power cable running roughly 1,640 feet from the surface.

What started as a joke between two people working in the mine became a guided sauna operation with seven ritual masters, a remotely controlled heater, mechanical ventilation and a plan for drying the room after guests leave.

First, carry a sauna into a mountain

“We carried most of the building materials underground on our shoulders,” Karlsson said.

He places the sauna about a third of a mile into the mountain and roughly 280 feet below ground. Adventuremine’s public tour page describes the descent as approximately 260 feet; Karlsson gave the more specific sauna depth in his reply. Either way, access shaped the construction before the first guest sat down.

The windows were a particular challenge. Karlsson described a team of 12 taking turns carrying the glass from the surface, with six carrying at once. Damage along the route would have meant more than replacing a pane at a building site. The replacement would have needed to make the same journey.

Inside, timber benches face broad windows onto the rock and water. Outside, the sauna sits beneath the mine’s exposed stone, with a platform and ladders leading into the lake. The photographs supplied by Adventuremine show how little separation there is between the finished room and the place it occupies.

A long power run, a fiber link and a fan switch

Karlsson identifies the installed heater as a Saunum Luxury with a 23 kW output and a HUUM control system. Power reaches the sauna through the long cable from the surface, and a fiber-optic connection allows remote heater control.

The air-blending system moves hotter air from near the ceiling into cooler air lower in the room. Karlsson says that makes more of the seating usable during a ritual and gives the team greater control over the heat guests feel.

There is also a local intervention: the team built a controller inside the sauna so the ritual master can switch the fan on and off manually. That lets the person leading the session change the airflow while remaining with the group.

“During our rituals, this allows guests to enjoy the whole sauna, rather than just the upper benches,” Karlsson said.

SaunaNews has covered how fan control changes the sequence of a Saunum session. At Adventuremine, the ritual master has the fan switch within reach of the benches.

The work continues after the last round

The mine is a cold, damp setting for a timber room. Karlsson says Adventuremine uses conventional mechanical ventilation, while underfloor heating maintains a minimum room temperature of 59°F throughout the year.

The stones have a second job after the ritual ends. According to Karlsson, the iron-ore sauna stones retain enough heat to keep releasing warmth for 24 hours, helping dry the sauna and bring relative humidity to 40% or less.

The retained heat and underfloor heating keep the room drying between bookings. Karlsson did not provide airflow rates or measured electricity consumption, so the energy cost of that approach remains an open question.

The audio system took development time too. Several speakers and a subwoofer sit inside the sauna. Heat, airflow and sound are all part of the room the ritual master works with.

Seven ritual masters and the Lady of the Mine

Adventuremine developed the ritual with Nordic Sauna Stories, drawing on the Lady of the Mine, the mythical guardian associated with miners and the underground world. Today, a team of seven sauna ritual masters leads the sessions, Karlsson said.

Guests arrive wearing helmets and headlamps. The walk through tunnels and chambers comes before the sauna rounds, music, storytelling and Aufguss. Between rounds, the lake supplies water at about 39°F. Food comes from local producer MurboAnnas, with cheese and charcuterie accompanied by a locally made non-alcoholic drink.

The operator’s current itinerary allocates about 45 minutes to the descent, two hours to the ritual and 45 minutes to the return. Getting people into and out of the mine is a substantial part of the visit.

That puts roughly 90 minutes of a 210-minute visit on the approach and return, or about 43% of the booked time. For staffing and scheduling, the journeys belong to the operation as much as the sauna rounds do.

As commercial social sauna expands, Adventuremine is a reminder of how much a venue’s program can depend on its location. The guides lead a group into a mountain, host the ritual and bring everyone back out. The sauna is one part of that whole visit.

“The mine itself is part of the experience,” he said.

Interview: Daniel Karlsson, Adventuremine founder and CEO, October 15, 2026. Photographs supplied by Adventuremine, credited to Adventuremine & Malin Englund.