Cities are environmentally unsustainable. Their "ecological footprints" depend on their level of prosperity, of course, but cities are in any case ecologically much larger than their own physical territories or metropolitan regions. Cities process large amounts of energy and materials, and they excrete different sorts of waste products. Do cities produce anything of commensurable or comparable value in return for the energy and materials they import, and for the residues they excrete? Are the internal environmental conflicts over these resource flows in cities successfully pushed outwards to larger geographical scales? It seems the more prosperous the city, the more successful it may be at solving internal environmental conflicts, and the more successful also in displacing environmental loads to larger geographical scales. At which scale(s) should (un)sustainability be assessed? In contrast to the deterioration of some North American city centers because of the process of urban sprawl, in Barcelona (as in many other European cities) urban sprawl has been compatible with increasing the economic and cultural values of the core of the conurbation. Tourism certainly helps, yet the Barcelona example begs us to ask: Which are the main environmental conflicts? At which geographical scale should they be comprehended? Should we travel to the nuclear landscape of southern Catalonia, should we go to Algeria and Morocco to see the gas pipeline, should we trace the route of the CO2 emissions from the Barcelona conurbation as they sink into the oceans or stay temporarily in the atmosphere, should we travel around the outlying quarters of the conurbation and listen to the complaints against noise from the motorways, against the threats of garbage incineration?.