I've blogged before about how great it would be to have a city with underground bike paths, replacing cars for most purposes. Almost everyone would ride a bike if they didn't need to worry about weather and traffic and hills. Even senior citizens would tool around in 3-wheelers with little effort.
It would also be great to have underground package delivery to your home via robots. Just order your groceries and whatnot via the Internet, then get an e-mail alert when the robot has delivered your goods beneath your home, in a sort of basement area that connects to the vast underground grid.
As you know, underground spaces stay at a consistent temperature, which allows you to put pipes in the ground and use the difference in air temperature compared to the surface for cheap heating and cooling.
In other words, there's a gold mine to be had underground. The big problem is that tunneling is expensive and dangerous and takes a long time. But what if we went at it another way. Instead of tunneling, we build our tunnel structures above ground and then pile mountains of garbage on top of them, for years, until the tunnels are totally buried. Then we build our city on top. No tunneling or ditch-digging needed. And that garbage had to go someplace anyway.
I'm assuming we have the know-how to keep the garbage smell and poisonous gas seepage from being a problem to the city dwellers above.
Worst idea ever?