20th Century Fantasy Novel that ISN’T Lord of the Rings (or for children)

Hi!

I’m looking to dip my toes into the fantasy genre. I generally prefer to read “classic” works before more modern works, but the obvious starting point (Lord of the Rings) is a bit too dense and long for me to want to commit myself to it yet. The problem is that it seems like most other classic fantasy works are aimed at a children or young adult audience, and those tend not to satisfy me as an adult.

So, I'm simply looking for any good fantasy novel that is from the 20th century (preferably 70s/80s or earlier) and is aimed at adults. I'm not opposed to more pulpy novels either, so long as you can vouch for its quality! Besides that, most of the novels I tend to read are crime, horror, or romance, so if you know of any fantasy novels with elements of those genres that would be cool too, but it doesn't have to of course.

Thanks for any recommendations you may have!