Background: The aim of this study is to measure the level of radon gas in the thermal springs of the four seasons in the Black Sea Region and to determine the gamma activity levels in the soils around them. Materials and Methods: Indoor radon activity concentrations of four spa facilities, namely Ladik, Havza, Ilıcaköy, and Ayder, were measured using CR-39 passive radon dosimeters and active radon monitoring AlphaGUARD for all four seasons. Radon activity concentrations in the soil in the vicinity of these spa facilities were measured using AlphaGUARD. Radionuclides in the soil samples collected from the spa regions were also determined using gamma-ray spectroscopy. Results: The highest radon value in the air environment in the spa facility was measured in swimming pools. Indoor radon levels in the spa’s swimming pool vary within a wide range, (30–2118) Bq·m⁻³. The average radon gas levels in the soil around the Ayder, Havza, Ladik and Ilıcaköy hot springs were measured as 38±1 kBqm^-3, 9±1 kBq m^-3, 50±3 kBqm^-3, 955±5 kBqm^-3, respectively. Conclusion: The annual effective doses due to indoor radon sources changed from 0.6 mSv to 13.4 mSv for workers, and from 1 x10-4 mSv to 3x10-1 mSv for patients. The annual effective dose equivalents from the soils around the spa were calculated to be between 82-558 µSv y-1. The results were compared with those of other measurements performed in different parts of the world.