You do realize that the cover in the shaft is underwater, right?! It gets disinfected within 720-750 milliseconds;) It’s much more hygienic than a roll-up cover on land or a sliding hall. This first year, we heated it to swimming temperature. We haven’t decided yet whether we’ll do that again next winter. Possibly just frost protection at 12 degrees. That way the cover can stay on the water. Or completely off and cover in the shaft. Thanks to the infinity pool, wintering is easier. All the technology is in the house anyway. Which sauna do you mean?? :p