There is a great need for applied studies at the K-12 level on how creative problem solving skills can be developed in out-of-school environments and what kind of learning activities can be used. Therefore, in this study, the effects of inquiry-based STEM (Science, Technology, Engineering and Mathematics) activities on students' STEM awareness and creative thinking skills in an out-of-school learning environment were investigated and the advantages and disadvantages of inquiry-based STEM activities were tried to be determined with student opinions. The study group of this mixed-method study consisted of 32 11th grade students selected voluntarily. Creative Problem Solving and STEM Awareness scales and a semi-structured interview form were used in the study. The findings of the study showed that inquiry-based STEM activities planned in an out-of-school learning environment improved students' creative problem solving skills and STEM awareness. Both qualitative and quantitative findings support that the activities improved students' problem solving skills and productivity and encouraged them to work collaboratively.