Underneath the whole of London is an untapped surplus of disused space in subterranean infrastructure - tube tunnels, exchanges, stations, and reservoir chambers. Ian Mulcahey, co-director of Gensler London, says “Now that London has reached the highest level of population in its history we need to think creatively about how to maximize the potential of our infrastructure. The adaptation of surplus and underutilized tube and rail tunnels could provide a quick and simple addition to our infrastructure network.” Gensler’s proposal brings back this ignored part of the city through the collective efforts of its citizens. By harnessing the kinetic energy of every one’s footsteps, a network of pedestrian and cycle paths with cultural and retail spaces is unlocked underneath the city. This self-sustaining approach to urban infrastructure is key to a carbon-neutral community, and London could lead the world once again in merging tradition with innovation to create a better future.