I found this place a couple of years ago. It is located on the corner of the street just past Hotel Panama Rey.
This medical clinic also has a massage center. I haven’t been there in a couple of years, so things may have changed. I remember the massage was about one hour. The massage therapists were equal to the ones I went to in the US. They also have a steam room and a shower, so you can steam yourself for a bit, then cool off in the shower and then have the massage. The total price was $25 (I think). I have had several Diet Cokes since then, so they may have altered my memory.