Here is a description that Jane Eyre gives of Thornfield in Chapter 11:
"All these relics gave to the third story of Thornfield Hall the aspect of a home of the past: a shrine of memory. I liked the hush, the gloom, the quaintness of these retreats in the day; but I by no means coveted a night’s repose on one of those wide and heavy beds: shut in, some of them, with doors of oak; shaded, others, with wrought old English hangings crusted with thick work, portraying effigies of strange flowers, and stranger birds, and strangest human beings,— all which would have looked strange, indeed, by the pallid gleam of moonlight."
This excerpt captures the gloominess and creepiness of Thornfield and plants in the mind of the reader the idea that the house is held captive by the past and its memories. The strange creatures that are featured on the hangings also create a sense of doom and eeriness.
When Jane returns to Thornfield from a walk, the house creates in her a sense of imprisonment. She says:
"I did not like re-entering Thornfield. To pass its threshold was to return to stagnation; to cross the silent hall, to ascend the darksome staircase, to seek my own lonely little room, and then to meet tranquil Mrs. Fairfax, and spend the long winter evening with her, and her only, was to quell wholly the faint excitement wakened by my walk,—to slip again over my faculties the viewless fetters of an uniform and too still existence; of an existence whose very privileges of security and ease I was becoming incapable of appreciating."
To Jane, Thornfield is a place of loneliness and confinement, and she refers to the invisible fetters, or chains, that she wears within its walls. She does not experience freedom at Thornfield or take advantage of its ease; instead, she feels walled in like a prisoner. This description provides a sense of how Bertha Rochester feels locked on the top floor of Thornfield.
Later, in Chapter 25, Jane Eyre tells Rochester about a dream she has had about Thornfield:
"I dreamt another dream, sir: that Thornfield Hall was a dreary ruin, the retreat of bats and owls. I thought that of all the stately front nothing remained but a shell-like wall, very high and very fragile-looking. I wandered, on a moonlight night, through the grass-grown enclosure within: here I stumbled over a marble hearth, and there over a fallen fragment of cornice."
Jane Eyre has a premonition of the destruction of Thornfield Hall. Though its walls are massive, she imagines it in ruins and only a shell of its former self. This is a foreshadowing of the fire that will destroy Thornfield.
The following quotes describe Thornfield and set the stage for the story. In many ways Thornfield is another character of the story, taking on different moods as the plot unfolds.
It was three storeys high, of proportions not vast, though considerable: a gentleman’s manor-house, not a nobleman’s seat: battlements round the top gave it a picturesque look. Its grey front stood out well from the background of a rookery, whose cawing tenants were now on the wing: they flew over the lawn and grounds to alight in a great meadow, from which these were separated by a sunk fence, and where an array of mighty old thorn trees, strong, knotty, and broad as oaks, at once explained the etymology of the mansion’s designation. - Chapter 11
Farther off were hills: not so lofty as those round Lowood, nor so craggy, nor so like barriers of separation from the living world; but yet quiet and lonely hills enough, and seeming to embrace Thornfield with a seclusion I had not expected to find existent so near the stirring locality of Millcote. - Chapter 11
"... I like Thornfield, its antiquity, its retirement, its old crow-trees and thorn-trees, its grey façade, and lines of dark windows reflecting that metal welkin: and yet how long have I abhorred the very thought of it, shunned it like a great plague-house? How I do still abhor—” - Mr. Rochester, Chapter 13