As climate change intensifies the frequency and severity of urban heatwaves, elderly populations are becoming increasingly vulnerable to outdoor thermal stress, particularly in dense Mediterranean cities. This study addresses the critical need for micro-scale, climate-responsive design strategies that enhance thermal comfort for aging residents in historically underserved urban neighborhoods. Focusing on the refugee-built area of Nikea in Greater Athens, this research explores the effectiveness of nature-based solutions (NBS) in mitigating extreme heat through spatial interventions tailored to the needs of older adults. Using ENVI-met 5.6.1, two scenarios were simulated: a baseline scenario reflecting existing urban conditions and an optimal scenario incorporating mature tree planting and water features. The results are analyzed across three key time points—morning, peak afternoon, and evening—to capture diurnal thermal variations. The findings demonstrate that NBS significantly reduce the Physiological Equivalent Temperature (PET), with peak improvements exceeding 14 °C in shaded zones. This study highlights the value of fine-grained, nature-based urban interventions in promoting thermal equity and supporting climate adaptation for vulnerable populations.