content: I recently took a course in hot stone therapy. Before I took the course, I looked into this product for use in the course. However, after deciding to go with the one offered by the instructor of the course, I am so glad I did. The basalt stones used in the spa have unique properties that allow them to hold the heat longer and they are made unbelievably smooth in "nature's rock tumbler", the ocean. If you are interested in this type of treatment, I suggest going to a spa, or seeking out a qualified hot stone therapist, and save your money on that product. The spa may cost a little more, but it will be much more satisfying! And if you are looking for stones to perform this treatment, go to the beach, and then go and buy an electric roaster!!