Let's Play SRPR - Volcano Castle Secret

If you try going up every pipe you see, you will end up in a place above the ground, and if you're not exploring enough you will miss the portal in the very same section. So that's the third portal we've discovered. Why are the Koopalings protecting them, anyway...? Rather, do they even KNOW there is such a thing outside their domains? Our questions will be answered as we push on...