To select the Arena you want to play, go to the Arena section. The Arena is loaded by clicking on or . The current game will be ended and a new one started. You can click on the button to restore the default Arena.
If you have self-made Clanbomber arenas, you can import them by clicking on . Granatier is looking in ~/.clanbomber/maps for the arenas. The default Clanbomber arenas are already shipped with Granatier.

If you select , a random arena will be used for each new round. If there are arenas you don't want to play, you can uncheck them.
