Super Mario 64 is almost 30 years old, but the game still has some secrets to offer, especially for those who are willing to dig deep. A SM64 community member named "Alexpalix1" has managed to open a sealed door that's bedeviled players for decades, not to mention countless children across the world in the late '90s.

As shown by YouTuber pannenkoek2012 in a recent video, the door in question is at the bottom of the cottage slide in one of the game's early courses, Cool, Cool Mountain. The door can be opened from the slide-side (which produces a Star), but since it lacks a doorknob, it remains stubbornly closed from the outside.

That is, however, unless you manipulate the mother penguin's position, flip between her, and then turn around so you can clip through the wall and open the door at the same time. If you're curious about the method, it has to do with some of the special properties associated with Mario's turn-around action. The video gets into more details, but all-in-all, it's quite an impressive find for one of the most-played games of its decade.