Super Mario 64/The Princess' Secret Slide

Once you get a star you can go to the room upstairs to the right. Enter the door. Inside you will find a room with three glass paintings. Jump in the one to your right.

There are two stars in this level:
 * 1) At the bottom of the slide
 * 2) Awarded if Mario finishes the slide in less than 21.0 seconds

To complete the slide in under 21 seconds, make sure to hug all of the corners. Do your best to never slow down by not hitting any walls.

There is a trick to completing the slide in even less time. When you reach the first corner, bump into the wall to turn yourself backwards (there is a coin that you can aim for to do this effectively). Note that it will take practice to do this properly. Now that you are sliding backward, bump into the railing on the right side as the walls end to bounce toward the left side of the slide. Immediately jump off of the left side and kick just as you reach the bottom of the slide level. It is possible to complete this slide in under 15 seconds.