This is probably one of my best kept secrets. I must've known about this for at least the last five years. Basically, there is a hidden secret easter egg in Kirby's Adventure, only to be found by the explorative type. Here's how ya do it.
Step 1: In level 1-2, get the cutter ability, and get to the place with the Warp Star on it, as shown:
Step 2: Get back on the platform where Sir Kibble (The cutter guy) was. Slowly inch along until the star disappears so that it's just barely offscreen, or it disappears, as shown.
Now, once you're in position, move back forward. If the star is still there, repeat the process, but throw some cutters off to the left. If it works, then just keep going forward.
Keep on going to the right, and you'll arrive at this super secret area! Whether this was intentionally allowed in the game by the programmers is a mystery to me, as this warpstar is the only one that appears to disappear like this in the game, so it does seem intentional. However, I could be wrong. Here's a snapshot of the room.