Our favorite thermal bath is Sole Uno near Basel. We go a couple times a year, often as a treat when we have visitors. They have indoor and outdoor pools with a variety of bubble massage jets. We particularly like the fire-and-ice pools, cold alpine waterfalls, and warm tropical rain room.
We like this thermal bath with kids, but note that under 4 years old is not allowed. My boys like going back and forth from the hot pool to the cold pool and timing who can stay in the cold the longest. They also like trying the different scented steam rooms with flavors like coconut/vanilla, lemon/orange, and mint.
I love relaxing in the the Dead Sea pool with 12% salt content, so you float very easily and relax. Of course, there are lots of massage jets and bubble beds, both inside and out.
We typically buy the 3 hour pass, which is plenty of time to relax and enjoy all our favorites. If you book a massage or other treatment, you may prefer a day pass.
Website: www.parkresort.ch
Location: near Basel - Roberstenstrasse 31, 4310 Rheinfelden
Open: daily 8:00 - 22:30