Who said it is not possible to venture past the ice wall? 
Well, for starters, you did.
The "Ice Wall" is simply an ice covered land mass that encompasses the known Earth. It is not literally a wall made out of ice.
If the ice wall encompasses the known earth, by definition, what lies past it is unknown. Therefore, no one has been past it. So how could this possibly be The Ice Wall if people have been past it?
If I encompass your known neighborhood with caution tape, does that mean that the rest or the world does not exist? I know you are just trying to be silly, but it seems to not be working for you.
Show me where I said nothing exists beyond a boundary?
I just stated that if the ice wall encompasses the known world, then outside that boundary is unknown.
Take your analogy for example.
If you grew up in that neighborhood, the known world would be encompassed by caution tape. However, if the mayor of the neighborhood decided to find out what was beyond the caution tape, and mounted an expedition, once this expedition crossed the caution tape, the known world has expanded beyond the caution tape. See what I'm getting at?
You can't say the ice wall encompasses the known world in one post and then the next post say that people have been beyond it.