How does Dickens's description of the chateau increase the suspense of the scene?
Good question. Our first impression of the chateau in A Tale of Two Cities sets the stage for all the other elements which add suspense:
It was a heavy mass of a building.... A stony business altogether, with heavy stone balustrades, and stone urns, and stone flowers, and stone faces of men, and stone heads of lions in all directions.
There is a "great door" which clangs when it shuts, and the hallway which runs from the door is
grim with certain old boar-spears, swords, and knives of the chase; grimmer with certain heavy riding rods and riding whips, of which many a peasant...had felt the weight when his lord was angry.
These intimidating instruments of killing are the first sight one sees after walking through the door.
This heaviness and stone and these instruments of death prepare us for the events which occur at the end of the chapter, of course. No sound outside the chateau but the sound of an owl and the trickling water in the fountain. It's a dark place, we know, since a servant must always carry a flambeau (lit torch) to light the way. There are dark passageways and winding staircases and big, heavy furniture.
Once the Marquis goes to bed, we hear horses rattling in the stables, dogs barking, and another owl whose sound isn't recognizable as an owl. We have more "stone" imagery--reminiscent of death, of course--and "dead darkness." The Marquis has become a stone face, as well. The sun rises and shines on those hanging instruments of death and torture, turning them blood red once again.
Dickens' use of imagery is clearly designed to create an imposing, dark, and suspenseful structure.