air conditioned public walkways. Who pays for it? For a small city, it might be feasible. A city the size of say Tampa? That's going to be very, very expensive. Not to mention, it's going to cost a great deal of money to keep the walkways air conditioned.
Underground tunnels. Going to be fun installing those around old pipes. ISPs have enough trouble installing fios lines, and you're wanting to install something that's going to be probably 8 foot high, and 6 foot across?
Above ground tunnels. Where are you going to put them?