The Dolder is ok, but nothing to get excited about. A nice, but small, indoor pool. Some nice saunas/snow room. A couple of very nice outdoor hottubs with a view over Zurich.
But if you are not a guest, it costs a bomb.
thermalbad-zuerich.ch is much better and about 1/10th the price. The problem is that it's so crowded, unless you go first thing Sunday morning or (apparently) late in the evening.
If anyone knows somewhere that is easily
accessible by public transport, within 1.5 hours of Zurich, I'd love to know. Bonus points if the place is child-free (sorry kids!).