This is Finnish-American country, and private hire here has a longer history behind it than the format has elsewhere. Duluth and Minneapolis hold the city end, with Eagle Harbor out on the shoreline.
Some are wood-fired and some electric, and the plunge is usually part of it. On the northern sites Lake Superior does that job.
In the Twin Cities & the Northland, 7 of the curated saunas fit this cut. See the full the Twin Cities & the Northland region guide for every venue, or keep scrolling for just the private saunas.
Every private sauna in Twin Cities & the Northland

Cedar & Stone Nordic Sauna
$$$Duluth, United States
FinnishFloating

Duluth Family Sauna
$Duluth, United States
FinnishSteam

Embrace North
$Minneapolis, United States
Finnish

Fulton Sauna
$$Minneapolis, United States
Finnish

PORTAL Thermaculture
$$$Minneapolis, United States
Finnish

Sauna Strong
$Minneapolis, United States
FinnishInfrared

Takka Saunas
$$Eagle Harbor, United States
Finnish