I turn to the dictionary for walls:
Among other things, I find immure:
Shut up between walls.

Yeah, that:

As in imprisoned, or,
On a lighter note,

As in intramural sports.
Ready to play;
Not ready to compete.

Shut up
Shut in
Shut out

Shut?

I remember a friend--
A lover once--
Who used to say

Get shut of

He meant set free from,
And he usually meant of things that hurt,

"Get shut of it, San," he would say
Until I thought I could
Step through pain that boxed me in

That was what he meant.

He got shut of me.

A decade and a half later I receive his gift:

Somehow these things
That close in
Also set free.

I stop here.
I can work with this.

These words
And a glass of wine
Will sing me to sleep

What are walls?
I am shut of them.

One Single Impression