You do not have to have a massage or any treatments when you go to spa, at least not at any of the ones I have been to. All the spas I have been to are centred round a swimming pool, jacuzzi, sauna, steam room and a whole lot of other water features that provide more than a day's activities without going near the treatment centre. As a family who love swimming and any associated activities it provides a day of rest and relaxation and, usually, a very nice lunch.
I was introduced to spa days by GN, I won a mother and daughter day at a spa near Newark. The prize included a massage so I had it and there was nothing unpleasant about it, but not enough going for it to want pay to have one again. However I have been back to the spa several times since and also to several others nearer home.