There's something very bourgeois about a group of guys hanging out in a delicious pool of steaming water. It is beyond medieval and very luxurious and this is how you will feel as you indulge in a thermal spa experience.
Eradicate your stag do hangover, detox your whole body with stints in the steam room and saunas, ready for the next onslaught of beer bashing, which could be poolside. You can add a muscle soothing massage to the mix as an optional extra but watching the cozzie clad girls around the pool might be relaxation enough.
It's all just a case of chillax with this experience as opposed to activity.