Space Day Spa
If your days in Sultanahmet are full of mosques and museums, this is a different kind of stop: a massage-focused day spa on the Asian side, in Kadıköy's Erenköy area. It is independent, not part of a hotel, and has private treatment rooms plus couples' rooms. The menu is mostly massage (Swedish, Thai, shiatsu, hot stone and others) with facial skin care as the one non-massage item. Google shows 4.6 from 323 reviews. It is closed on Tuesdays, and you must reserve before you go. Prices and treatment lengths are not published on its website.