Kid Niki is full of hidden passages and bonus stages, some of which are... different.

Like take this spot in Stage 4, for example. It's the platform directly after the second moving platform.

Jump up a few times and the next platform will turn into a fish!

Walk off the platform, directly into the fish's mouth and...

You're in!

You traverse the length of the fish (there's nothing in it but bones), and you come to the exit

Well, how else did you expect to get out of a fish?