The game is played on a map resembling an office desktop. The player must stop a set number of enemies, known in the genre as "creeps," from reaching a set point on the playing field. This is accomplished by building and upgrading towers that shoot at, damage and kill the enemy creeps before they are able to reach their objective. Unlike many other tower defense games, the path of the creeps themselves is not set; instead, the towers built determine the path of the creeps, who take the shortest path they can find to the exit. The game prevents making an exit inaccessible.