I'll consider books with at least 50 years, as a rule of thumb to consider pieces that have impacted and endured multiple generations. As a personal rule, it should also be a book that I read some years ago and still resides in my usual thoughts, creeping in while I'm daydreaming or thinking about a personal situation. I haven't read many of the books here mentioned, although it seems I have read most of the more often mentioned.
Alphabetical order:
"Crime and Punishment", Fyodor Dostoevsky
"Jane Eyre", Charlotte Brontë
"Wuthering Heights", Emily Brontë
Like so many others here, I'm fond of gothic fiction.