30km south of Rotorua on the SH5, there’s a place called ‘The Thermal Wonderland’. It has the Lady Knox Geyser here. Go in if you like and look around, the colours are meant to be awesome, but if you can’t afford it and want a FREE thermal swim, 200 Meters down the road from the entrance and car park there’s a small wooden bridge.
Park up and go for a swim in the pool. Two rivers meet, hot and cold. We spent almost 2 hours in the water (and that was on a very cold rainy day)