The Water Wheels
Don't climb down the ladder yet; go to the end of the path, where there is railing. Here there is a crate and a lever. Pull the lever, which lowers a chain nearby, and push the crate down into the water. Drop down into the water after the crate. The ladder you didn't climb down leads down here into the water, and there is another one directly across from it. Pull the crate over to that ladder, climb onto it, and then climb up the ladder.
When you reach the top, pull the lever over on the right; this will open the door blocking your way into the Water Wheels. Drop back down into the water and swim through the large doorway, bringing the crate with you. Find the chain you lowered earlier, and pull the crate under it. Climb onto the crate, then jump up and grab the chain. Climb it and then look for the track in the middle of the platform at the top. Push the gear on the track all the way back from the edge to connect two large wheels. This starts a wheel at ground level rotating. Drop back down into the water, and make your way over to it, the nearest shore is just next to the large door you opened.
Note that the wheel has large bars protruding sideways, which move up and down as it turns. Stand under the lowest part of the wheel (i.e. under the center), facing opposite the bars' direction of movement (referring to the bars two feet over your head, of course, not the ones way up in the air). When a bar is at the lowest point, jump forward to grab it. When you are above the platform the wheel is attached to, let go.
Follow the platform to the left a short distance to find that it doesn't lead anywhere. It ends at a large pillar against the wall. Notice that there is a narrow ledge on the pillar just above head height, with a pipe a short distance above that. Climb onto the ledge as you have done before, then jump up and grab the pipe over your head. Shimmy right over to another pillar. There is a break in the pipe along the way, but if you just keep shimmying right you'll be ok. When you are as far right as you can get, drop down onto another platform.
Follow the platform out to a fairly narrow pipe. Walk across this to another platform, which is next to another large pillar. This part of the pillar is cylindrical, and has a pipe running around to the right. Grab the pipe and shimmy around the pillar to another small platform on the far side, then let go. The pipe you were just shimmying along turns vertical and continues for a short distance. Right next to it is another pipe that goes up a long way further.
Grab onto this pipe and climb to the top. At the top, jump off, and you will land on a chain. Turn to Ico's right and look ahead of him to see another chain. Swing back and forth a bit and jump over to it. Now do the same again, and this time you will land on a metal platform. Go through the small tunnel on Ico's left to the wheel on the far side.
Now you have to grab the moving bar and ride it to the top as before. This time when you let go you will find yourself on a long metal walkway. Follow it to the end. Near you is a wheel which serves as a large circular platform, which spins around. Jump over onto it. Run (or get taken) to the far side, note a nearby ladder on the way, and jump to the next spinning platform. Jump from this onto the sideways spinning platform, run to the far end of it, and run straight off it onto solid ground. If you fall at any point, find your way to the ladder near the biggest wheel. It can be a pain to climb as the wheel may knock you off, but it's the only way back up except to start again. The camera will spin around now, stay still so as not to run the wrong way. Once it has stopped follow the path you are on off to the right and down, and then out onto the rocks.
Follow the path out of the cave to find yourself on a narrow path near the bottom of a waterfall. Follow the path up. The path turns off to Ico's left, and then does a U-turn to follow a lower route. Then it ends. When you reach the end of the path you have to jump the gap. If you are in the habit of holding the stick while in mid-air to help him jump further, as I am, don't this time, as the camera angle switches fairly madly during the jump, and you may jump him into the ocean. On the far side continue to follow the path.
Written by Crumplecorn