MIT News published an article recently hypothesising that early humans may have cooked their food in hot springs. They didn't have any compelling evidence, so I was sceptical, but people on HN dug up some interesting accounts that suggests this could be true:
From HN user tzury:
In the Talmud they refer cooking in the Hot Springs of Tiberius in a casual manner that makes the impression it was a regular thing to do.
Rúgbrauð (Icelandic pronunciation: [ˈruːɣprœiθ]) is an Icelandic straight rye bread. It is traditionally baked in a pot or steamed in special wooden casks by burying it in the ground near a hot spring, in which case it is known as hverabrauð or "hot-spring-bread". https://en.m.wikipedia.org/wiki/R%C3%BAgbrau%C3%B0
here in tamsui in taiwan they cooked eggs in the hot springs