The present contribution, reports on the results of ongoing research efforts on performance assessment of a number of buildings designed by the Austrian architect, Konrad Frey. He is a pioneer of energy-efficient architecture, and his designs, those dating back to the 1970s, adapted the principles of modern solar houses. The current study focuses on the Kindergarten Hart, which was especially designed focusing on the availability of cross ventilation option in building. For the purpose of analyzing thermal comfort, indoor air quality, and the occupants’ adaptive actions with respect to natural ventilation, we conducted long-term monitoring under summer and winter conditions. The monitoring efforts covered indoor and outdoor environmental conditions, as well as the state of windows. Thereby, study of the monitored dataset provides a better understanding of the building performance. Moreover, it makes it possible to examine whether the architect’s expectations in terms of thermal comfort and indoor air quality levels are fulfilled or not. In addition, investigation of the occupants’ interactions with windows, together with indoor and outdoor environmental conditions, assists understanding of possible associations between the window opening/closing and environmental parameters, as well as potential optimization of the control-oriented actions.