Soleron on 10 June 2009
Well, this is a glitch, but if on SM64 you fly up to the highest bit of red sloping roof at the very front of Peach's Castle with the Wing Cap, you can fall through the roof and land in the space behind the castle main door. If you then go "through" the door, you'll be in the space behind the interior door. I found it through many hours of just flying around the Castle.
