For those unfamiliar, John Bellairs wrote quite a few YA gothic novels, usually centered around a youngish boy partnering with an old professor or librarian to solve a potentially world-ending mystery. I find they hold up well, and I still love reading them to this day. I haven't read many other books that scratch that itch, YA or otherwise.
I think his highest-rated book is The House with a Clock on Its Walls, so if you are interested, start there.
by Magicians_Nephew