Proximity is a central concept in the contemporary urban planning debate on making cities more sustainable, but it often overlooks the diversity of the cities and their inhabitants. In different urban settings, the meaning of proximity and the possibility of implementing it may widely change. Moreover, different individuals have different accessibility needs and possibilities depending on manifold demographic, socio-economic and health features. The chapter discusses the multiple meanings and dimensions associated with the proximity concept by examining accessibility-by-proximity and demographic ageing in Santiago de Chile, an unequal Latin American metropolis. The chapter examines the potential that Santiago's ageing neighbourhoods have for promoting proximity locally, also considering the quality of the public space through which urban inhabitants move to access close opportunities. While the concept of proximity can reorient urban and transport planning towards more environmentally sustainable outcomes, the elements discussed in the chapter highlight the social justice issues that may limit the positive impact of proximity for different population groups.