‘The metaverse’ does not yet exist. It merely exists as many different visions of a future of computing, especially a future that Meta and Mark Zuckerberg would like to shape. Meanwhile, the history of computing has been marked by visions of augmented or virtual reality. At the same time, many media-technical elements of the metaverse-to-come already exist, such as games engines or VR glasses. This course therefore deals with visions of metaverses and their current media-technical instantiations. It explores some of the back stories of current and future metaverses, takes a critical look at current media, technical, social and economic aspects of existing offerings, and offers practical experiences of virtual worlds and the tools used to build them.