Transylvania appears both at the beginning and the end of Dracula. Bram Stoker presents it as a foil to England, the home of most of the heroic characters. England is presented as modern: science and reason rule the day. In contrast, Transylvania is ruled by religious folklore and appears primitive in comparison.
When first coming into the country to visit Count Dracula, Jonathan Harker notes in his journal that he has read of the mighty superstitions of the inhabitants of the Carpathian Mountains before embarking on his trip. He finds this to be the case when interacting with the locals, who anxiously cross themselves when he brings up Dracula or his castle. Before leaving for the castle, the innkeeper's wife tells Jonathan that he must not go. This brief passage of the novel fully illustrates the gulf between Jonathan's rational incredulity and the superstitious nature of the Transylvanian population:
“It is the eve of St. George’s Day. Do you not know that to-night, when the clock strikes midnight, all the evil things in the world will have full sway? Do you know where you are going, and what you are going to?” She was in such evident distress that I tried to comfort her, but without effect. Finally she went down on her knees and implored me not to go; at least to wait a day or two before starting. It was all very ridiculous but I did not feel comfortable. However, there was business to be done, and I could allow nothing to interfere with it.
Jonathan accepts a rosary from the innkeeper's wife just to calm her nerves, but little does he know that she is right to fear the count.
Dracula's castle offers no relief from this sense of the ancient. Described as crumbling and Gothic, the castle represents almost primordial evil, the sort that modern people try to reason away. The castle's atmosphere gets to Jonathan, and even he, with all his rationality, concludes that "the old centuries had, and have, powers of their own which mere 'modernity' cannot kill."
So ultimately, the book's impression of Transylvania is primitive and sinister. The populace lives in fear, and the vampire count reigns supreme. This allows for a greater contrast once Dracula goes to England, where he initially seems to overcome the forces of modernity to prey upon the populace.