Whenever gamers are presented with a door they feel they should be able to open but can't, then you'd better believe it's going to trigger some serious emotions.
That's certainly the case with a door in Super Mario 64's Cool, Cool Mountain level. The door in question is all the more interesting because it's not a 'fake' door that leads nowhere but one which you actually exit once you've completed the slide portion of the stage.
Nintendo's designers certainly didn't want players to be able to re-enter this hut because they removed the door knob from the outside of the door model. However, the door is still there, and you can actually re-enter – it's just that the hut has been designed so that its external barrier goes beyond the door, preventing Mario from touching it and thereby triggering the door opening animation.
Now, in a video by Pannenkoek2012, it has been shown that it's possible to re-enter this door without resorting to a hack – something which hasn't been done in the past 28 years.
The tactic was discovered by Super Mario 64 speedrunner Alexpalix, and involves grabbing large penguin located nearby and using it to glitch through the hut's invisible collision barrier which prevents you from touching the door.
It's amazing that players are still discovering secrets like this in video games that are almost thirty years old.