Go to Whiterun and walk a few paces after you enter the gate. Turn around, and there should be a short staircase leading left and right. Take the left one and immediately after you go up the stairs there should be a opening in the wall to your right. Inside should be a barrel. Jump on the barrel then jump to the far side. Make sure that when you jump that you do so to the right slightly so you do not hit your head. After a few attempts you should stick to the side. Keep jumping and you should get over the wall and out of the map.