Amethyst Hot Springs is a hot pools business in the small settlement of Harihari, Westland, holding a Google rating of 3.9 from 66 reviews. It sits on the South Island's west coast, a natural stopping point for travellers working their way between Hokitika and the glaciers.
Natural hot pools are partly a game of weather: how hot the water runs can shift with rainfall and the seasons, so the same pool can feel perfect one visit and tepid the next. Small rural soak spots tend to be simple — basic changing space, your own towel — and the milky tinge of spring water is dissolved minerals, not dirt. Regulars aim for quiet times of day, keep soaks to fifteen or twenty minutes, and ease in slowly after a long, chilly drive down the coast road.
For a roadside township like Harihari, a warm pool before continuing south is about as West Coast as it gets.