They are located south of the Villarica volcano that heats water pockets, converting them into thermal water springs.
The owner took advantage of a small creek in which there are multiple springs of thermal water. Each spring has a small pool constructed, having all different temperatures which are marked. Emanating water at 80º Celsius (176 Fahrenheit) mixes with cold water from the creek lowering it by less than half.
To avoid damaging the environment, they also constructed elevated wooden corridors that take you between the 20 pools, generating the geometric form that gives its name.
As you enter the resort through a wider part of the creek, you will see the strong green Nalca leaves (Gunnera Tinctoria) covering the creek and contrasting with the red painted corridors and constructions.
Almost all of the geometry points have the pools or small huts to change where you can leave your clothing. At the center there is a restaurant where you can eat superb pizzas. At the very far end a cold waterfall that people rush to enter after staying in the hot pools.
I made quite a few images of this colorful Termas Geométricas.