According to a medieval legend, in 1345 a mysterious light would have fascinated the citizens of Manresa (Catalonia, Spain). For their medieval eyes light was much more than an optical phenomenon, it was the focus of philosophical, mystical and metaphysical reflections. Light was considered the origin of life and “the principle of all beauty” (Robert Grosseteste). The low tech video art piece “That mysterious light”, proposes a dialogue with medieval thought that invites us to ponder about the role of light in our current lives, in a context characterised by excessive energy consumption. Through sound and visual textures, the relationship between light, nature and thought is explored.