Secret ending Achievement
Around halfway through the game (and right after you finish the boulder level for As fast as possible (50G)), you will reach a level that ends with an obvious broken ladder hanging above you. The only way to reach this ladder is to backtrack and grab some dynamite, then bring it to the broken ladder. Place it directly under the ladder and let it explode. This will drop the ladder down, allowing you to climb up. Reach the end of this linear section to unlock this achievement for this secret ending.
*IMPORTANT* After obtaining this achievement, choose to Continue your game. You will be back at the top of the broken ladder. Climb back down and proceed out the right side of the level to complete it like normal, allowing you to proceed through the rest of the game to obtain the rest of the story achievements.