On some boards where there are mountains surrounding the areas you can have your chosen soldier walk up to certain creases in the slope going up the mountain and have him walk up the mountain. It does not work on every spot so just move him left to right while walking him forward and once you find the right spot he will start climbing upward. Now do not give up at first if he falls before the top, but keep trying, moving the joysticks to certain angles until you get it just right. Once at the top you will end up in limbo outside the playing area and can wonder freely around the outskirts of the play area without being detected, and can also take out the enemy in most cases without ever being noticed. Be careful in certain parts of limbo where there is play area land on your map, for when you switch to another soldier and switch back you will be back in the play area. Also for what its worth, the first board where you start, the mountains on this board cannot be climbed as far as I have tried.