Ranong is one of these places rarely visited. It's next to Burma and is a major gateway for travel across the border, but not so much for foreign visitors, more for Burmese migrant workers.
There's quite a few hot springs in Ranong, Its not that we have volcanoes and magma, but the mountains here are being pushed up and the pressure squeezes the water making it hot.
That pool at the top, it's for looking not for swimming. A wall nearby has the only word you need to recognize, 65 Celsius will easily scald.
These hotsprings feed cooler pools, that you can bathe in, overlooking the river below. The guard at the pool tells me the river is quite dirty and its better to use the hotsprings for bathing. He warns me against the pool at the front, says its too hot right now, it needs time to cool down.
A bridge overlooking the river lets visitors explore the nature trail behind. Better to do this first, then if you get bitten, any insect bites can be soothed by the hot water.
You can find it on the map below.