Fourth world of Switchball, first four levels, getting a gold medal in every level.
There's a hidden path in level 3 but it's kind of out of the way. You basically follow the way like I did, except you grab the jumping thing and push the block out of the way as you're actually supposed to do, then when you roll down there's a platform moving under you, jump on that and then jump into the pipe where it stops at and just follow it.
