<p>Edu-Metaverses are Metaverses intended to foster education by exploiting eXtended Reality technologies and collaboration. This paper proposes and evaluates an Edu-Metaverse using immersive Virtual Reality to promote cultural heritage sites. The proposed system involves: (i) the creation of a virtual environment that represents a real-world natural environment; (ii) the embedding of educational content regarding local cultural heritage into the virtual environment to foster informal learning; (iii) the implementation of a multi-user persistent space, enabling users to connect and engage with the virtual environment. To investigate the possible differences between individual and collaborative informal learning in the proposed Edu-Metaverse, we conducted a between-subjects study involving 52 participants. Results show that collaborative learning improves the knowledge gain and retention of concise cultural heritage content. No significant differences were instead found between the two conditions for discursive content. The results are discussed considering: (i) the sense of presence in the virtual environment, which was not significantly different between the two conditions; (ii) social presence, which was expectedly higher in the collaborative condition; and (iii) activations per session of objects providing educational content, which were higher in the collaborative condition for concise content, while discursive content showed no significant difference between conditions. These results suggest organizing educational content into several concise pieces of information to exploit the benefits of collaborative learning in immersive Virtual Reality Edu-Metaverses for cultural heritage.</p>