The hike to the termas is a 2 day hike that you can do from Puerto Varas easily on your own.
From the Lonely Planet site you can download the complete Book “Trekking in the Patagonian Andes“ in digital version, or for less money just a part of the book where you’ll find the description of the whole Trekking Termas del Callao.
If you want to make this hike and you read the description, “Al Sur Expeditions” is offering you a nice Kayak solution about how to get to the starting point of the hike.
Guided tours:
Trekking Paso Desolación: Al Sur Expedicion
Trekking Reserva Nacional Llanquihue: Al Sur Expedicion
Trekking to Ralún: Kiñehuen Expedicion
Trekking to Cayutúe Lake : Kiñehuen Expedicion
Trekking Kiñehuen : Kiñehuen Expedicion