Go to the checkpoint (sand vortex) that is named "The underground reservoir" Get through this area, and when you get to the rope that leads you out, don't climb out, there is a platform around the middle of the rope, swing there and press jump. You will find yourself in a series of traps. Go to the one in which spiked bars appear in the wall and when the bars retreats, wall run up and press jump. You will find yourself on a bar that stretches vertically, climb down the bar until you find a bar that stretches horizontally. Swing on it and jump. Do this again and again until you find yourself on another platform. Find a broken door, strike it three times and proceed. To get back, go the way you came and climb out of the reservoir.