The invisible playground at the root of Pianta Village...
Okay, so it's not a "playground" per se, but it's freakin' cool nonetheless.
While trying to guess which episode 100 gold coins were on Pianta Village (which might be the least fun I've had with a videogame in years), I found myself sliding down the tree trunk. I usually just consider it a lost cause, but I was especially frustrated so I spastically jumped and twisted. Amazingly the usual "fall" didn't happen. I was somehow able to slide and jump all the way to the bottom to an invisible black platform at the bottom of the level.
WORD.
As you'll see in the video, you can look up at the underside of the village which has to be a good 1/2 mile away. You can also look outside the borders and see Pinna Park from semi-underneath. And the coolest thing is, you can't fall off. It's a boxed-in invisible mess of Mario fun.
Let me finally add that it could take you one try or thirty to recreate this glitch. It's not easy. The first mushroom I slide down in the video, you actually want to land on - and then try jumping towards the root and butt-stomping before the "fall" takes over. Also, if you're trying it on a level with your waterpack - DON'T USE IT. It's like an automatic "fall" inducer. You gotta do it old school...
Super Mario Sunshine
Movie 1 (4.4 MB Windows Media File)