It is quite real while you have your eyes open, but if you are not looking at it the barrier doesn't exist at all.

It's the same way with many other evils in life; they seem to exist, and yet it's all seeming and not true.

You will notice that the wall--or what we thought was a wall--separates the Munchkin Country from the green country that surrounds the Emerald City, which lies exactly in the center of Oz.
There are two roads of yellow bricks through the Munchkin Country, but the one we followed is the best of the two.

Dorothy once traveled the other way, and met with more dangers than we did.

But all our troubles are over for the present, as another day's journey will bring us to the great Emerald City." They were delighted to know this, and proceeded with new courage.