This article focuses on the development of an educational outdoor adventure mobile app while presenting findings that were derived from various case studies that we conducted using it. The mobile application, called RouteQuizer, is complemented by a web application and a database, forming a system that enables teachers to create educational treasure hunt activities for their students and monitor their performance. The aim of the research was to create a system that would exploit all possible Outdoor Adventure Education (OAE) and treasure hunt benefits while excluding possible smartphone use negative consequences. The development of the system took place in Greece and began in December 2017, by conducting a nation-wide research examining Greek secondary teachers' Information and Communication Technology (ICT) literacy and perceptions on smartphone use and outdoor activities. By June 2018, 700 questionnaires were collected. In order to test the system, in March 2018, we conducted a pilot case study in Lesvos island Greece and between July 2018 and February 2020, we conducted four additional case studies and a teacher training program, all of which took place in Lesvos island Greece. During the development process of the mobile application, we focused on the participatory aspect of the process, paying special attention to the teacher and student evaluation during the design and prototyping phases. Considering that the system is educational we research whether the mobile application provided effective learning outcomes and whether it benefited students' social and physical skills. The results that we collected suggest that the mobile application is an effective learning tool while mobile learning and treasure hunt benefits have been repeatedly confirmed during the case studies. Greek teachers and students also proved to be capable smartphone and computer users, and reported being willing to participate in similar activities in the future.