It suddenly hit me the other day what it is that I really enjoy about going outside.
I am of course talking about Doom.
As you explore the dingey, maze-like military complex of Doom's first episode, you're occasionally blessed with a window to the great outdoors. But actually venturing outdoors is very rarely the correct path; it's nearly always a secret area, accessible only through some hidden door. Oftentimes there's no way outside at all, so you're always left wondering if an area is reachable or not.
This leads to what I have termed (as of now) the "Out of Bounds" phenomenon: a feeling of awe bestowed when the player reaches a destination that they previously thought was inaccessible.
This is what has always captured me about those outdoor areas: a feeling of mystery and intrigue, as if somehow I'm not supposed to be here.
As I pondered this, I realised that many other games make use of the Out of Bounds phenomenon - even dating as far back as Super Mario Bros (1985). You all know the bit I'm talking about: the secret warp zone that you can only reach by going over the level. At first you think, "Whoa, is this a glitch? Am I supposed to be able to get up here?". And then you realise that it's an intentional secret area, and your mind is blown.
Portal is another game that uses this to great effect. All of the secret areas have a certain "forbidden" feel to them, complete with dirty walls and ominous graffiti, as if you've stumbled into a room that the game never intended for you to see.
I've always really enjoyed finding secret areas in games, and now I understand a little more about why that is. Perhaps I'll use the Out of Bounds phenomenon in my own games in the future...