I know very few people in the world have access to hot springs, but I just thought people here might find this information as interesting as I do.
Japan:
Cooking Eggs:
In some other places, hot-spring pools can become a neighborhood egg-cooking spot. In Japan, these eggs are called Onsen Tamago (温泉卵), and are slow-cooked in the natural spring water.
The result is a unique custard-like texture in the yoke, while the whites are soft.
“It is said to have originated in Onsen Towns in Beppu, Oita prefecture. It is said that the first Onsen Tamago was made over 300 years ago when a traveler left his eggs in a hot spring by accident and found them cooked when he returned." MyFormosaFood
More Info:
Steam Cooking
“It is a cooking method using high-temperature steam heat gushing from hot springs, and it has been used in Beppu since the Edo period. Just put the ingredients in a basket, put them in a pot where steam of about 100 degrees called “Hell Steaming Kettle” and cover it.” | Jigoku Mushi
At tables equipped with timers and hot-spring powered steam cookers, you can steam your own food.
Heating Greenhouses:
“Hot springs are used to heat greenhouses for different types of fruit and vegetables. At Atagawa Spa on the Izu Peninsula, the Atagawa Tropical & Alligator Garden cultivates tropical plants like banana trees and bougainvillea.” | Nipponia
By piping the heat into radiators, they can heat and humidify the greenhouses with no electricity.
Iceland:
Volcano Bread
Cooking rye bread with the help of a volcano has a long history in Iceland. All you had to do was dig a hole near a hot-spring, place the dough (which is in a container) in the hole, and burry it.
The boiling water will steam the dough to a dense but soft texture.
Hopefully you remember to mark where the hole is, but if you did, you will have freshly cooked bread with no need of an oven. As an extra bonus, you can also cook some eggs when you are there.
More info:
Oh right I completely forgot about tamagoyaki, probably because it’s not pure egg, it has other ingredients mixed in too. But yes, those are thoroughly cooked!