Pleasant and clean. Slightly too many stars for that place tbh, but it's all you need from a sauna
If you're in Sofia for an extended amount of time, you may want to consider buying the "Multi Sport Pass" like I did. This gym is one of the nicest that is accepted by the pass and offers gym (which isn't overly crowded) with nice equipment (both cardio and weights), thermal services (sauna and steam room), group fitness classes with many classes a day in a nice studio space and pool. This is the nicest gym I've found around Europe over the last couple of months. They offer free towel service and lockers too.
Unkind staff, electrical wardrobe not-working, everything uncomfortable and dirty. Swimming pool ambient not warmed-up and very chaotic with music/swimming course/water fit classes, all at the same time while the poor customer is looking for calm and relax. Sauna and steam bath the only little heaven, but literally and unexpectedly "little" (three very small rooms) for a wellness centre with the word "spa" in the title and that is promising you "thermal bath". There are in fact no thermal pools at all. Not-recommended.
One of the best spa places in Sofia
Very nice swimming pool
Very satisfying swimming pool.
relaxing areas
There is often too much chlorine in the pool. It is not a warm place. The fitness is modern, the thermal places are OK.