How does the house make such an impression on Lily?
What would you think if you saw a bright pink house? That alone made a big impression on Lily. Lily describe this as,
...a house so pink it remained a scorched shock on the back of my eyelids after I looked away (67).
Before Lily even enters the house, she describes all of the plants around the house and says, "The smell could knock you over (68).
When Lily enters the house, she says that she felt "a travelling current that moved up my spine" (69). This is because she knows somehow that she is close to some knowledge about her mother, which was the main reason she has run away.
Of course, as she takes in the house, there are many unusual and interesting elements, for example, the intense smell of furniture wax, many mirrors, and most importantly, the statue that will be so important to her, Our Lady of the Chains, which makes her feel like "I could see through to something pure inside (71).
There are other aspects of her first visit that impress Lily, too, of course, and if you read that section of the book carefully, you will see them.