Termas de Huife is located a few miles outside of Pucón, on the banks of the crystl-clear Rio Liucura (Liucura River). The termas function for as both a full service health and relaxation spa for day visitors, and as a resort for those who choose to spend the night, in either of two types of accomodation, cabañas (cabins) or suites. It's set into a beautiful narrow valley and has a nice combination of natural foliage and landscaping.
There are two outdoor thermal pools which maintain a temperature of approximately 97 degrees Farenheit. There is also a cold-water pool for those who like the back-and-forth between hot and cold water, as well as private thermal bathtubs and whirlpools-for-one. There's also a hydrotherapeutic pool. Adventure activities such as canopy (ziplining) also make an appearance here, and the grounds are extensive, with 300 hectares of land, though the rooms are all close to the well-appointed restaurant, which offers special meals for those who have dietary restrictions.
The crowd here is both Chilean and international, and it's considered a good spot for families, so if you're traveling with kids, its a great place to go. If being around children detracts from your holiday, you might want to just spend the day or choose another spa, of which there are many in the area.
Day passes cost less than US $25, but the transfer to the termas if you don't have your own transportation (and there really is no public transportation to speak of here) will set you back about another $30, if not more.