This glitch is very easy to do. Simply put a lone grenade turret on the ground, on its side. Get in, rotate the turret and aim so that the camera goes through the ground. Jump, and if done correctly, Banjo should fall through the ground. Doing this under Spiral Mountain and selecting a vehicle that can float, you can explore and find some evil eyes that are smoke that come out of a LOG's factory (though it is hollow).