When you visit a spa, you should be prepared to undress completely for massages and body treatments. Most spas provide paper panties for modesty, and they also provide robes and towels. Depending on the treatments you receive, you may need to change into a new robe if it gets dirty or damp. When it comes to what to wear under the robe, it really depends on what type of massage you are getting and what you are comfortable with.
If you are getting a messy treatment that includes wraps, mud, or oils, your therapist will provide disposable underwear so that yours doesn't get wet or dirty. Most spas also provide plastic slippers or flip flops for guests to wear during their visit. You should not wear outdoor shoes near damp and thermal facilities, as guests will walk barefoot in these areas. At some dedicated spa retreats, it's OK to wear baggy pants and a t-shirt, but if you're staying at a hotel with a spa, the hotel's restaurants will have their own dress code.
If you're a woman on the big side, rest assured that spa robes are usually cut very generously, and there must be plenty of tunics for you. If you're small, however, you can get lost in a mountain of towels. Now, going completely naked under a robe is preferable, however, you can keep your underwear (if you are a woman, taking off your bra is essential) if you don't feel comfortable being totally naked. So what should you wear under those tunics? Well, it really depends on you and the massage you are going to receive. The answer is that “Spa clothing doesn't seem to vary much from one spa to another, and most places provide a robe and slippers upon check in.
