My wife and i spent all day at Therme Geinberg and had a fabulous time. We swam for nearly 7 hours in the various pools, our favorite being the cascading pools, which are also the hottest. We had a fantastic meal at the main restaurant and found it very affordable. However, the drinks are extremely overpriced (6.45 euros for fresh orange juice) so i would definately recommend bringing your own water at least. Also don't make the mistake my wife and i made and forget your sandals, flip-flops or what have you, because it is very slippery in the halls etc.
The pools were amazing though and our favorite part was the jets that shoot out of the beds in the bottom-most cascading pool. We could also see a herd of sheep while we swam in that pool, which i thought was cool. The smaller round pools next to the main indoor pool are not hot-tubs like i thought they would have been but only luke warm pool. My mother-in-law who came with had a 50 minute massage for 50 euros, which she enjoyed immensely, and she enjoyed the saunas alot too. My wife and i just stayed in the pools though and never got bored just swimming around and relaxing.
i would recommend this to anyone, especially when it's colder outside, it was in the 50s fahrenheit outside today so it was a nice contrast, although we plan to go back in the dead of winter preferably with snow falling around us.