There is so much parody in these few chapters.

I thought it would be a pity not to mention this 'fun' part of Catherine's disappointment ( and a parody of the reader).

UDO;
'There' said Montoni.....'is Udolpho.'
Emily gazed with melancholy awe upon the castle it was now lighted up by the setting sun, the gothic greatness of its features, and its mouldering walls of grey stone, rendered it a gloomy and sublime object.

NA;
No such announcements for Catherine with;
'There' said Henry....'is Northanger Abbey.'
She waited with impatience for the first awesome view;
CH 20;
..every bend in the road was expected with solemn awe to afford a glimpse of its massy walls of grey stone, rising amidst a grove of ancient oaks, with the last beams of the sun playing in beautiful splendour on its high Gothic windows.

What does Catherine get instead of a beautiful setting sun in which to observe the Abbey?
A sudden scud of rain, driving full in her face, made it impossible for her to observe... LOL!

UDO
Emily continued to gaze, till its clustering towers were alone seen, rising over the tops of the woods.

NA;
Catherine on the other hand was in the abbey ;
...without having discerned even an antique chimney.
So low did the building stand.

Udo;
At length the carriages emerged upon a heathy rock, and, soon after, reached the gates, where the deep tone of the portal bell, which was struck upon to give notice of their arrival, increased the fearful emotions, that had assailed Emily.

NA;
...there was a something in this mode of approach which she certainly had not expected. To pass between lodges of a modern appearance, to find herself with such ease in the very precincts of the abbey, and *driven so rapidly* along a smooth, level road of fine gravel, without obstacle, alarm, or solemnity of any kind, struck her as odd and inconsistent.

UDO;
As the *carriage wheels rolled heavily* under the portcullis, Emily's heart sunk, and she seemed as if going into a prison.

Na;
Catherine on the other hand was springing from the carriage with the help of Henry;
... without feeling one awful foreboding of future misery to herself, or one moment’s suspicion of any past scenes of horror being acted within the solemn edifice.

This comparison makes me chuckle at a 'reader' who would expect anything straight from a book.