There are many such places in New Zealand that use the natural waters that bubble underground as theraputic waters--like Teddy Roosevelt used back in the day.
Here are some facts I found about the place we go to in New Plymouth.
The Historical Tarawhata Hot Mineral Baths were exploited following the search for oil in New Plymouth in. In 1909 the Bonithon Freehold Petroleum Company drilled a 3004ft (1 kilometre) well. They found no oil, but plenty of warm mineral water, which ran to waste until 1914. Then J Solomon, of New Plymouth built a 25 metre by 12 metre bath house which was used as a public swimming pool, as well as several private baths, all of which were enclosed in the same building.
In the mid 1960's the baths closed to the public. In 1999 the Bonithon Spa Health Co.Ltd re-established the Historical Bath House to a 5 star Mineral Health Spa.
If you still want to know more, follow the link below.
I think this might be the best gift yet!