Side Passages

   

Let's create a passage leading to the right. The right wall goes away, and in its place we see the back wall of the next square over (plus some other walls that don't have textures).

   

Similarly, a passage leading upward looks like this.

   

There can also be passages leading left and downward, but let's skip those and look at a passage that leads … inward! We can only do that in four dimensions, of course.

   

As three-dimensional people, it's easy for us to confuse inward with forward, but they really aren't the same thing. The original wall is still right there in front of us.