How does Lemony Snicket use imagery in The Miserable Mill?

Imagery:

Like the other buildings in town, it had no windows, just a round door in the center. But it was the way the building was shaped, and how it was painted, that made the Baudelaires stare. The building was a sort of oval shape, with curved, skinny sticks sticking out of the top of it. Most of the oval was painted a brownish color, with a big circle of white inside the oval, and a smaller circle of green inside the white circle, and some little black steps led to a little round door that was painted black, so it looked like an even smaller circle inside the green one. The building had been made to look like an eye.