This small room has a chain from the ceiling. Start up the chain - monsters will come. Go down and kill them. Then go back up the chain to the idol door. Ignore it and go down the hole. You'll see Yorda through a grate. Step on the spot on the right to open the door and call to her. She'll come to you.

Now make her stand on the other one. Go through the other door. Climb up the pipe and jump across the open spot back to the grassy area. Go over to the hole and call to her. She'll jump up to you and climb up. Now go open the idol doors.

The Ico Walkthrough

Please swing by my Forum to ask me how to get through if you're stuck somewhere I haven't put up yet. I'll get back to you quickly.