Once you cut the would you will see one long a little orange box, four arrows and a spike in the middle of the arrows. rotate the spike until the flat part is face up. us the arrow to left and right to rotate. leave it flat side up. drag spike on top of the orange box. if nothing happen, rotate the spike with the flat side still face up. drag over to the orange box. one of the four sides while the spike is face up will work. You want the orange box to turn into two boxes moving in the opposite direction.If you get it to do that once the box are aline with each other tap it. do it three times and the box will move. You will have to rotate the spike again on it four sides while the spike's flat side is still faced up. You will do this four times (four time the orange box move). then bridge will be made.
It's not really a cheat, but more of a hint. At the top part of the lake, go to the island in between the two waterfalls. Go to the blocks sticking out on the map (press L or R) and face south. You should eventually get the option to jump. This brings you to the lower section. By doing this, you don't have to fight the bats in the cave everytime.
NOTE: THIS ONLY WORKS WHEN YOU ARE GOING DOWN. GOING UP, YOU HAVE TO GO THROUGH THE CAVE!