RTA Guide/The Princess's Secret Slide
The Princess's Secret Slide is located above Whomp's Fortress in the lobby, in the rightmost painting. 1 star is needed to access it without a lobby BLJ.
First Star Tutorial
This star is spawned when the slide is completed in under 21 seconds. It's recommended to get this star first, because if something goes horribly wrong and you don't complete the slide in time, you can still get the box star.