Walk up the incline and onto the platform. Go over to the switch and pull it to lower a chain out toward the center of the reservoir that Ico needs to climb up on. Pull then push the block over the edge and into the water. Have him climb down the ladder and jump into the water. Swim over to the box and press the 'Circle' button to nudge it toward the other side being mindful of the stronger currents. Head toward the ladder on the other side. Once the block is reasonably near it, climb up on the block and jump onto the ladder. Head on up and move to the lever and pull it to raise the gate that was blocking the entrance to the reservoir. Jump back into the water and head for the box. Push the box through the gate and on straight ahead into the reservoir. Continue on until the chain that was lowered by the first lever is in view (use the 'Right' mini-joystick to help locate it if necessary). Once you have the box in reasonable proximity to the chain (note that it will stay in position), climb onto the box and jump on the chain. You're now done with the box. Climb up upon the platform and push the device on the track forward, so that it engages the water wheels on either side, transferring power from the one on the right to the one on the left.

Jump back into the water (yes it's a long way down, but he can do it) and swim back toward the gate that the second lever opened. As Ico passes the wooden structure on the right, there's an accessible area between the structure and the gate, which Ico should head over to and climb up onto. Continue over to the slowly turning water wheel and walk slightly past the center point, then turn and face the direction that it's turning. Wait until a peg is a bit in front of Ico than have him jump toward it and grab on. It's not difficult to do! The wheel will carry him up and around to the top and across a platform. Press the 'X' button to drop him off onto the platform. Walk along the platform away from the wheel toward the stone wall of the cave. There's a barely visible ledge on the left side below the pipe that he can jump up on and from there up onto the pipe above it. Have him do so then slide to the right until Ico drops down onto the other part of the pipe that's been broken away. Continue right until he can go no farther on the pipe, then have him drop to the next platform. It's connected via a larger diameter pipe to the following platform.

Have him carefully drop down on the pipe and slowly cross it. When he nears the next platform, he can jump onto it, which should save a precarious step or two. Have him jump up on the pipe that circles the cylindrical structure and slide around to the other side on it until he drops off. Next have him climb up the vertical pipe as far as he can. Make him jump off backwards toward the chain behind him and he'll turn and catch on near the bottom. Note the second chain off to the right, which is his next destination. Orient him so that he's facing it and start him swinging. When he's moving at a good clip, have him jump at the end of an arc onto the next chain. Now repeat this process continuing in the same direction and jump onto the platform. Walk through the short corridor over towards the other slowly turning water wheel. Have him grab onto a peg in a similar fashion to the way he did so on the first one and ride it up to the top, then drop off onto the wooden platform above. There's a faint shadow to be seen when he's over the platform, that can be used as a guide for when he should drop. Follow the wooden pathway to the right and around to the end.

Jump from there onto the first of two vertically rotating cylinders. Head over to the next one and jump onto it. The third cylinder is revolving on a horizontal axis and is thus a little more difficult to jump onto and traverse. The trick is to land on the center of it, then run along it using a little bit of right movement of the left mini-joystick to keep him near the center of the top if he starts to fall off on the left and a little left movement of the left mini-joystick if he starts to fall off on the right. To do this get a bit of a running start from the left side of the second vertically spinning cylinder and then jump onto the center of the horizontally spinning cylinder. When he gets near the end of it, simply jump up on the platform beyond. Be careful not to jump too far or too near the end or he'll be back in the water and have to restart from the box near the first chain. Once he's safely on the other side, have him head to the right and then down the short wooden walkway and off to the left toward the light at the end of the tunnel.