The study presents the results of a pilot implementation of the Content and Language Integrated Learning in OpenSimulator Project-CLILiOP. Content and Language Integrated Learning together with constructivism provided the theoretical basis of the project. A multi-user virtual environment was developed using OpenSimulator, which entailed a tour of the students' avatars on a virtual island where they viewed and exchanged information in the English language regarding geographical terms and concepts. The project's duration was ten weeks. A total of 105 students participated, divided into three groups: one used the application, the second was taught the same cognitive material using a conventional teaching method, but still under the scope of CLIL, while the third was conventionally taught. Results indicate that the learning outcomes of CLILiOP were better compared to the other two teaching methods, but also underline the need to further investigate the uses of 3D multi-user virtual environments in second language learning.