After you had full healing/life lengthened then run on the wall in front of the hole that you entered and press jump again.
Strike it with you great sword once and it will break, and then proceed. Drop down and you will find various obstacles (ledges, beams, and a bar) Swing on the bar and press jump. Run at it so that you are hanging on the space between the railings.
To your right, you see a small bit of railing missing. To get this, you must start out beside the checkpoint (sand vortex) that is named 'Farah, come back'. To get back, go the way you came and climb out of the reservoir. Find a broken door, strike it three times and proceed. Do this again and again until you find yourself on another platform. You will find yourself on a bar that stretches vertically, climb down the bar until you find a bar that stretches horizontally. 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 in a series of traps. 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.
