ELI5 Saunas - how do near boiling temperatures not burn you?

Do Saunas and Steam rooms offer any actual health benefits? Do they help one’s skin? What happens to your body in a sauna? How can I sit in a 85 degree celsius sauna and not get burned, while water of the same temperature would scald badly? What is the Finnish connection? How do wood structures in saunas not rot or get moldy?
... we explain like I'm five
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