Okay, I see where the platform is. It's actually not the room on the 2nd floor next to the blue star, it's the last room to the right of the stairs. You go into the room, go onto the wooden platform. Look up, and there is the platform above your head.
Question: What is a wall jump??? How do you do it? I read instructions to wall jump on the wall to the right, I have no idea what that means. I've tried triple jumping, can't seem to get to a point where I can hold on and pull Mario up. I've tried wall kicks (jump to wall or press against wall and kick it), and I've tried backflips, no good.
I got up there once YEARS ago, trying to figure it out for my kids. Someone help!