You make it to the last part of the journey, the porch. The bigger house has several porches, but this one has the least altitude, also just so happens to be nearly parallel with your treehouse. It also just so happens to be the one you most travel, as you go to the kitchen just inside.
This door in front of you was placed both by you and your sister as a remembrance of all your ancestors who couldn't live in your ancestorial home. Your mother included.
Your mother died shortly before the Human fell down into the underground. She was so close in fact, that your sister was busy buying flowers to place on the grave to help you with the widely referenced disproportionately small gap. Brazing the new world, your older sister took you under her wing, for better or for worse.