I've rewritten this to handle any arrangement of walls! Now you can explore whatever open spaces you like. Here's a demo walking around the default title card letters in first person!
As always, here is the json:
First Person Maze.zip (7.0 KB)
The perspective gets a little squiffy, especially for walls visible 2 tiles away, but I think the brain makes sense of it. Or maybe just mine does because I've been staring at it so long!
It also has that classic effect from a flat draw distance that means you can see further in the diagonal directions. I've played enough videogames that do the same to not worry myself over that 
Possible further ideas floating around my head: Add a compass, add visible character sprites/items, draw different walls depending on the tile name, (e.g. doors), turn the default top-down view into a "map" accessible from a menu (where maybe walls only become visible on the map if you have been near them), try some random room generation... or maybe just optimise the current code 