Avoiding invisible walls & Sudden Death Syndrome

[Reactor]

I believe it's high time for a topic like this, as more and more games utilize these nasties, which combine creativelessness with lazyness. I'm talking about the level designers' methods of forcing the player into a linear corridor, and forbiding him to explore the level, or choose a direction other than the intended route of level completion. Invisible walls are the softer method, Sudden Death Syndrome is the harder one.
Sure most of you are all very familiar with invisible walls. The recipe goes like this: "We don't want to go here and there, or climb this and that thing, because that means we would have to design extra level branches, place more textures, even design secret areas, and secrets are the work of Satan itself, and creating more than one route for a level would probably KILL us all, so we put an invisble wall there, the player can't explore and that's final!". At even more harsh games, going anywhere else the game developers wanted you will outright kill you, making sure you won't even dream about exploring and focusing anywhere else than dead center. Damn annoying to say the least.

While this policy is disgusting as can be, at several occassions - mostly at outdoor levels - some kind of boundary must be established, but I still feel that using the invisible walls or Sudden Death Syndrome to confine the player within an outdoor level is a nasty semi-solution only. I would like to hear some ideas for outdoor levels, how to build up boundaries without using these nasties. I'm talking about various environments, let it be a temperate field level, a forest level, a snow and icy level, and especially a desert, where there is sand everywhere for millions of kilometres. So far, I used fences, cliffs, perhaps some chasms or some other barrier which'd understandably kill the player (like an ocean). I was wondering, are there any solutions for outdoor levels?

[wildweasel]

What about insurmountable chest-high fences?

[kodi]

A river would be pretty useful as an alternative to cliffs in an open environment. Barricades and overturned busses are a staple in cities.

[Reactor]

Hm, wrecked vehicles are perfect solutions in city levels! I haven't thought about this before, and it's fully plausible.
Fences can work in most environments except deserts, where no one with a right mind would build a fence

[Ravick]

For city maps, also fire actors can be used. Earlier versions of "Armagedoom" make uses of this, for example..

For hell maps, lava rivers are the best.

For deserts, maybe rocky outcrops, or high dunes. Or maybe just allow the player to freely walk by giiiiants empty sand fields, but let him see the goal he must reach.It'd be tedious to explore such ruge areas of nothing, and he'll rush to get where you want him to go.

[Reactor]

I was wondering is it possible to give some "wrap-around" rules for such big open outdoor maps. You know, where the player goes on and on and on, and still keeps returning to the same location. Many games utilized it, though in Doom it would result in nasty things, like a thrown projectile flying forwards for all eternity across the level.