http://oyster.ignimgs.com/mediawiki/wiki-api.ign.com/the-legend-of-zelda-skyward-sword/2/2f/Sword_1872.jpgIn Lanaryu mining facility, the south side of the platform north of link's icon. If you fall off there (at least for me) you land on an invisible platform maybe 10 feet down. It has to be a drop down and not a jump. The platform extends from the wall to ~5 feet out from the wall, and about ~30 feet left and right. Link will then jump off it and fall into the pit.
What makes this so horrendously annoying, is if Link falls off, he respawns back on the invisible ledge instead of the real platform. You can't run up the wall to grab the real platform, so the only way I've found to get off it is restart the game or kill yourself using bombs. (Thats the method I had to use as I hadn't saved in quite a long time)
This might be useful somehow if theres other invisible ledges like this... But it's probably a fluke.