It’s gone through maybe around 200-250 ice baths and saunas during this year alone. I usually cover it with my other hand when in sauna to not expose it to extreme heats (altho at that point it’s frozen from the ice plunge lol), but not that religiously. Zero problems so far. The ice plunge is still around +4 Celsius so it’s just cold water. Sauna is way hotter than the Apple’s rec for the Watch.

Sauna. Ice baths. Meetings. Naps. Cooking. Easily My most used daily feature of Apple watch.