This is a book I read in the early 90s and I have almost no details. I just remember I found it at the school library, and it featured a kid finding a miniature city underground, and pricking his finger on an ornamental snake fang statue and passing out.
This is one of the books I was looking for that originally led me to Stump the Bookseller! Assuming we’re talking about the same book, it’s “Through the Hidden Door” by Rosemary Wells.
That’s what I would say too. I’ve used this website to find that same book too!