There are armutalan baths and beldibi turkish baths in marmaris. I have been to both and find armutalan to be good.
They have a swimming pool outside which you can use if you want (as do beldibi), then when you go in you can go in the jacuzzi, steam room, have a facial, oil massage etc. You can book direct with them if you want or just book with
ICR as its easier than faffing about booking yourself.
I got married in turkey and we went to the turkish baths for my hen party. It was really nice and relaxing and leaves you so chilled out. Would definately reccomend it.