Immediately to the east of Wall is a high grey rock wall, from which the town takes its name. This wall is… — Neil Gaiman

Immediately to the east of Wall is a high grey rock wall, from which the town takes its name. This wall is old, built of rough, square lumps of hewn granite, and it comes from the woods and goes back to the woods once more.

There is only one break in the wall; an opening about six feet in width, a little to the north of the village.

Through the gap in the wall can be seen a large green meadow; beyond the meadow, a stream; and beyond the stream there are trees. From time to time shapes and figures can be seen, amongst the trees, in the distance. Huge shapes and odd shapes and small, glimmering things which flash and glitter and are gone. Although it is perfectly good meadow-land, none of the villagers has ever grazed animals on the meadow on the other side of the wall. Nor have they used it for growing crops.

Instead, for hundreds, perhaps for thousands of years, they have posted guards on each side of the opening on the wall, and done their best to put it out of their minds.

Source: Wikiquote · CC BY-SA 4.0