INTRODUCTION: URBAN FACETS'How can I not know today your face tomorrow, the one that is there already or is being forged beneath the face you show me or beneath the mask you are wearing, and which you will only show me when I am least expecting it?', 1 acclaimed Spanish writer Javier Marías wonders in the first volume of the monumental novel Tu rostro mañana (Your face tomorrow), whose central theme is betrayal, as well as the relationship between face, foreboding and knowledge: evil, when it arrives, arrives with a face that we had already intuited under its mask, but that we had instinctively chosen not to perceive consciously, as though obeying a supreme imperative according to which it would be atrocious to live with the deep certainty of what the face hides. The same could be asked about cities: Could we survive in a city, for example in one of the cities that we visit as tourists, if we knew what is hidden under their masks? Those which they don at every step, either spontaneously or -and such is the case of the most visited cities in the world -because their faces have been carefully made up in order to convey an image, as urban marketing would say, but also, as the quote by Javier Marías suggests, in order to hide their true faces, or at least some of their deep layers? Those that, under the masks, are presented to the tourist, to the traveller, to the business professional, layers where a bitter and treacherous truth is often hidden?Talking about the face of a city is a fruitful metaphor, since it allows one to distinguish between the project of a planned and conscious visibility and the underground tingling of deep and painful features, hidden by the brushstrokes of urban makeup. The pimples, the wrinkles, the dark circles of a city do not appear to the distracted visitor, the one who is carried away by the illusion of a superficial splendour, and only emerge as almost imperceptible signs, for perceiving and interpreting which one needs a sharp and sceptical look,