This study is based on the hourly thermo-hygrometric measurements carried out between July 2nd and December 14th, 2018 at three points in the Cacica Salt Mine and at two very close points between them outside the salt mine. iButton sensors were placed at -75 m (two sensors) and -41 m (one sensor) inside the salt mine and at an average altitude of 437 m outside the mine. We monitored for a period of 166 days (3984 hours) the inter-monthly, inter-diurnal and inter-hourly evolution of air temperature, relative humidity and THI bioclimatic index inside and outside the mine. Inside the salt mine, the microclimate is characterized by a relative thermo-hygric uniformity and a slight discomfort by cooling. The inter-hourly maximum amplitudes of the air temperature and relative humidity for all hours ranged, for all monitoring points inside the mine, between 0.4 and 2.1°C, respectively between 18.2 and 31%, while outside the mine the equivalent values were 41.9°C and 66%. The THI inter-hourly amplitudes ranged from 0.4°C to 1.5°C inside the mine, while outside the equivalent value was 39.1°C. The thermohygric uniformity of the salt mine microclimate is also evidenced by the standard deviation values of the hourly data which are very low into the mine (temperature: between 0.1 and 0.3°C; relative humidity: between 3.2 and 5.8%; THI: between 0.1 and 0.3°C) compared to the equivalent outside values (8.2°C, 11.4% and 7.9°C), respectively).