The objective of spa is to relax people but none of knowledge would prove how to design to make people relax. It is found that if people have a good thermal comfort condition, human body would feel relax. From 25 famous spas in Bangkok, appropriate comfort for human perceptions of touch, visual, and sound, would make body relax. Only 3 selected spas were evaluated in details. It results that activity and clo-value are fixed variable. The dependent variables are 1) air temperature, relative humidity, wind speed, and mean radiant temperature (MRT) for touch, 2) illumination, intensity, reflection, and contrast for visual, and 3) sound pressure level for sound. Data were collected from 25-30 people as random selection to find out the comfort condition of each factor in 3 selected spas. It is found that 3 selected spas have: air temperature around 23 D 27 oC, relative humidity 47-55 %, and 23-28 oC of wall surface temperature, 0.9 m/s of wind speed, 25-27 oC of floor surface temperature as mean radiant temperature impact, 2) 3-17 lumen/m2 of illumination of wall, 3-9 lumen/m2 of ceiling, 2-4 lumen/m2 of floor, 1-5 cd/m2 of intensity of wall, 1-5 cd/m2 of ceiling, 1-2 cd/m2 of floor, 26-47 % of reflection of wall, 34-62 % of ceiling, 41-70 % of floor, and 1:3 of contrast for picture, and 3) 45-58 dBA of classical music. Thermal, visual, and acoustical properties were analyzed and used for a spa prototype design. Then, the spa prototype was tested by 25 people randomly. With 0.2-0.25 clo-value and 0.8 MET, the conditions of each factor are: air temperature around 26 D 27 oC, relative humidity 46-49 %, and 27-28 oC of wall surface temperature, 0.9-2.9 m/s of wind speed, 25-27 oC of floor surface temperature as mean radiant temperature impact, 2) 16-63 lumen/m2 of illumination of wall, 8-85 lumen/m2 of ceiling, 4-7 lumen/m2 of floor, 5-52 cd/m2 of intensity of wall, 5-78 cd/m2 of ceiling, 1-3 cd/m2 of floor, 31-82 % of reflection of wall, 62-92 % of ceiling, 33-42 % of floor, and 1:3 of contrast for garden, and 3) 51-54 dBA of natural sound or classical Thai music. As results, whenever body feels comfort from touch, visual, and sound with less clo-value and 0.8 MET, it would relax and enjoy spa.