Starting from a ruin situation, this tiny 4-story building located in Barcelona’s old center, had to become a place to live. As all floors slabs were removed, and the building was seen as a slender prism formed by heterogenous masonry walls, the idea of leaving them exposed became conceptual: these walls are a museum of the building's history, and any trace of its construction/use will be left unaltered. A sheet of glass will separate the new slabs from the main façade; the stairwell will be a 4-story void linking the entire interior and showing the surprising height of such a slender building