It should not be able to do that at all. Is there any other steps leading up to that you're leaving out (or are you sure you commented on the right game)?
I used the ceiling texture for the page background; if you're not seeing that then it's a wall.
Also, pressing down doesn't turn, it just moves back (I can add that, though either are common)
Thanks for your help.
What happens is that as I enter the dungeon the view seems to turns up from this : https://img.itch.zone/aW1nLzU2NDcyNjIucG5n/original/Hdtmgu.png
to this (and then stays this way) : https://img.itch.zone/aW1nLzU2NDcyNjkucG5n/original/f%2BKucB.png
Turning left or right gives this : https://img.itch.zone/aW1nLzU2NDcyNzUucG5n/original/pQTz9M.png
EDIT : replaced the images with link.
Yeah, it should not be able to do that. Do you know your version of Windows and your graphics card? I'm not sure if I can do much on my end, but I'll still try to look into it. The only thing I can think of is maybe there's something going on with the rendering (MV isn't really build for 3D so I wouldn't be surprised)
