You can play a practice game on different maps without having to be online when you do this. Go into the game menu with the "Single Player", "Multiplayer Internet", etc. options. Click on "Multiplayer LAN" (even if you do not have a LAN), then click on "Host Game". Input your game name, set your "Players Limit" to "1" and continue with the remaining settings. Make sure you have a different map than "CNC_Under.mix", then click "Start Game" You will be able to blow up bases and do everything that you could normally do in a regular multi-player game.