I walked up to the final door, turned round so I was looking down the hallway and walked backwards. After a while walking back for a while, if you veer left or right, you will fall off an invisible path into oblivion.
I guessed that it was unintentional.
That kind of thing happened often in games I used to test on Playstation 1 and Dreamcast many years ago. The gaming boundaries being improperly defined in certain places.
If you want to add something relating to this glitch, you could always have the same bunch of rooms but in reverse behind the endgame picture, so if someone does what I did, all they will do is find themselves back in the hallway.