<p>The thermal environment of urban public spaces is becoming increasingly prominent. As a mountainous, high-density city in southwestern China, Chongqing’s unique landscape and dense viaducts have fostered riverside parks and under-bridge parks, shaping diverse microclimate spaces for recreation. Field monitoring of microclimates in different outdoor activity spaces in the riverside and under-bridge parks in Chongqing during winter and spring analyzed the relationship between visitor numbers and thermal comfort, and explored the influence of thermal comfort on recreational activity types. Findings: (1) In spring, the thermal comfort in under-bridge spaces is enhanced compared to non-under-bridge spaces, with the thermal perception in under-bridge spaces reaching up to “slightly warm,” while the thermal perception in non-under-bridge spaces can reach “warm” even “hot”. (2) In winter, visitor numbers at most of the outdoor spaces increased with rising PET values; conversely, they decreased with rising PET in spring. (3) thermal perception significantly influenced activity occurrence probability. When thermal comfort is “Cool” or “Slightly Cool”, people prefer low-intensity activities. When “Neutral”, all activity types occurred readily. When “Slightly Warm”, probabilities increased for fitness activities and social activities. The under-bridge spaces narrower thermal comfort range encourages fitness/ social activities. (4) The non-under-bridge spaces maintained some activities at “Warm”/ “Hot” thermal perception with facility support. Based on the research findings, design strategies for microclimate adaptability are proposed, including the establishment of seasonally responsive facility optimization measures and dynamic activity guidance mechanisms for winter and spring, to enhance the recreational experience and urban space vitality in mountainous, high-density cities.</p>