Anyone remember the waterfalls in the magical room number 2 in the Crystal Caves? There is a +5 HP mushroom that is hidden. Your view of it is obscured by the waterfall, it would be in the line of sight of a char looking straight ahead, but the player looking from a bird's eye view cannot see it, you literally have to walk up and down the three unit thick waterfall and try each area.
Amazing secret lol.
Here is a screenshot, cuz it's just so insane haha.
http://www.4shared.com/photo/AmfKZhWj/lol.html