This Could Work,

in London and I guess many other cities,

that have disused rail systems under them, the plan involves putting disused subways into use and making them in to underground walk and if big enough cycle-ways in sections of the Underground system, architects at Gensler, the firm behind the idea, developed this proposal that looked to address a series of issues including bicyclist fatalities on surface streets, a lack of pedestrian public space and the general ease of movement across the city, the great news is that unlike many other proposals much of the system is already there, many of these stations have been deserted and boarded up for decades – some for nearly a century, and others (attached to since-abandoned lines) were never opened to the public in the first place, over time, some have been used to shoot commercials or scenes from films, and others have had wartime uses as shelters or for stockpiles, what a waste of space right under our feet in overcrowded London! and many other cities I guess.