One of the strong ideals of Modernism is Mobility.The Modernist urban design thus derived, from designs by New York architects of 1920s, to post-war English architects of the Archigram style, repeat the architectural scene of footbridges criscrossing amongst gigantic buildings.These never get realized, until in Central District of Hong Kong, where arrays of footbridges were built that links internal public spaces and arcades in many private buildings, creating a real multi-strata metropolis, fulfilling the dream of Modernist architects and planners, testifying that Architecture for Mobility indeed drives urban lives.This article moves onto study cases of recent major renovations of footbridges and indoor public spaces in Central, to illustrate how the understanding of their social history and appreciation of their original architectural designs, form the basis of innovative conservation, revitalization, and even re-organization of these commercial public spaces and routes, enabling better and easier utilization of this multi-strata pedestrian system, and thus points the way to sustaining this architectural legend.