the platform with marbles that you have to sink down a hole.
You start with one platform, one marble, one hole, then it increases from there. I have finished it on beginner and on advanced (all yesterday) and now I'm moving on up. There's one style of platform that totally messes me up, but as long as I can make it past those, I do great. It's a fun/challenging balance game that's supposed to help with posture and alignment apparently. For me...it's a break in between hoola hooping (which is INSANELY strenuous btw) or the running games.