Raising young people's interest in studies and careers related to science, technology, engineering, and mathematics (i.e., STEM) is an important societal concern both at European and global level. We argue that the creation of attractive and engaging STEM learning environments necessitates involvement of learners, educators, parents, and STEM professionals in their design. In this paper, we will present a study in which primary, lower and upper secondary school students, teachers, school directors, parents, and STEM professionals in Finland (n = 27) and Greece (n = 24) were invited in the participatory co-design of a hybrid (virtual, physical, formal, and informal) STEM learning environment. The aim of this paper is to present, first, a method employed for the participatory co-design, and, second, display the results from Finland and Greece regarding participants' shared wishes on teaching, learning, assessment, and motivation both in general and in relation to STEM subjects. In addition to recorded focus group discussions with these stakeholder groups and researchers, data were gathered by means of an online survey with open-ended questions which participants filled out during the co-design sessions. Data were analysed based on grounded theory approach and qualitative coding techniques. Amongst the most commonly shared wishes between different stakeholders in both countries raised during the sessions were the importance of connectedness of studies with students' life as well as the use of diverse teaching methods such as collaborative and ICT-enhanced learning. The results of this study are discussed towards to the creation of a pedagogical framework and design principles guiding the development of a hybrid learning environment consisting of components such as a social web platform, e-portfolio, robots, serious games, entrepreneurial tools, and digital radio connecting various stakeholders with an aim to increase youngsters' interest in STEM studies and careers. The results will also contribute to the understanding of how to raise interest in STEM in general. The study is a part of a broader European research project funded by the European Union's Horizon 2020 research and innovation program with partners in Belarus,