Go to Spiral Mountain and use a Wing Pad to fly and land on the stone Grunty hat. You can then use the Feathery Flap to land on an auto-slide hill (you'll automatically slide when you land on it). Jump so that you go around the hat, and then use the Feathery Flap again to put yourself in the space between the mountain and the lair! So I guess it wasn't as big as it seemed.
Submitted by: Kenjoki-Ikari