In a place called Waimangu park. this whole areas in a valley which is called volcanic valley, it was created by the eruption of, you guessed it a volcanic, not really that long ago like the 1890's. and it's an areas that is still very much active, and of course with a active geothermal areas comes hot pools.
This is a fairly large one, and it's is striking blue caused by the minerals in the water.
The Waimangu Park is well worth a visit if you find yourself in New Zealand's north island and close to Rotorua. It is a strange park, huge and not as well known as some of the other parks in the area, and very limited with visitor numbers, they let in like 25 people a hour or something like that so you can really appreciate the nature the way it should be not overrun with crowds.