Hot stone massage is great for relaxing sore, tired muscles. The stones should be warm enough to feel nice, but not uncomfortably so or too hot that they leave marks. Everyone has a slighly different temperature threshhold so your therapist should be checking in with you to make sure. Also, don't be afraid to speak up and let your therapist know if the stones are too warm or not warm enough. I clean my stones (scrubbing each stone & the roasting pan) in warm water with a peppermint soap right after each treatment.