The MinetopiaSDB plugin has support for teleporters that let you easily travel through the entire city.
To select a position for the teleporter, execute the following command:
After you've executed that command, you can create a teleporter by looking at a sign and executing the following command:
/teleporter create <Name on sign> <Costs> <Min. Level>
You can remove teleporters by breaking the teleporter sign. To make a teleporter usable, you need to place a heavy weighted pressure plate below the sign.