My girlfriend and I love thermal bath and spa and we would like to visit one or more of these places in our stay in Switzerland. Is there any list of the available baths/spa and their characteristics?
A Swiss online resource I know is this one. It lists a lot of Spas in Switzerland that are worth a visit. I quickly checked it, and all I know of are on the list. Unfortunately the list is in German, but at least some of the further links are also available in English.
If you're looking for an English resource I would recommend this site. It also lists a lot of Spas in Switzerland and also here I could found all spas I know.
I personally can recommend Therme Vals. It is a little bit out of the way, but it is really beautiful and also from an architectural point of view worth a visit.
I'm not sure about spas, but if you're interested in hot baths, there are quite a few in the lake Geneva area (the area I'm familiar with):
(Note: I've only ever been to the first two)
Main selling point is that you can combine the slopes and the hot baths. One of the best days out I ever had was sledging followed by hot baths followed by a fondue aux bolets!
Time limited (3 hours, by default), no babies or toddlers (4+), expect queues on weekends with bad weather...
And something completely different... If you happen to visit Geneva, then you could try going to "Bains des Pâquis". Located in the very city centre, on the Geneva lake, this place allows you to relax in sauna/hammam, swim in the lake and enjoy delicious fondue afterwards.
Booking in advance is recommended. Also check the opening hours. This association closes relatively early.
Another nice place I visit is Leukerbad
There are mountain activities (e.g skiing during winter, hiking during summertime) and two good public bath:
If you plan to stay more than one day, a pass can be a solution as it gives free entrance to both bath (unlimited time) and to the cableways (Torrent and Gemmi).
After it depends as well if you have small children, on the second bath, they only allow children from 8 years old and further but is more quiet and less crowded. We really enjoyed it with my wife: it is perfectly romantic as well :)
For people with a smaller child I recommend to go only to the Burgerbad Therme because they even accept babies in some parts.
There are also other bath in some hotels, but I never tested as it is reserved for the customers only.