This Kickstrter (looking for a new kick) wants to turn an abandoned section of the New Your Subway into an underground park.
Sounds kind of cool & unworldly. Kinda sounds like the underground city in the movie, A Boy and his Dog.
If this works in NY, maybe it's something we could replicate in some of the northern tunnels of the abandoned Cincinnati Subway, maybe under the "protected" bike path.
It would be a good use of utilizing space. Normally people build up but we could take advantage of the tunnels and build down.