I don't know how I managed to miss Alan Garner's The Weirdstone of Brisingamen when I was a kid, because I would have loved it then even more than I did yesterday, which was a lot: gripping plot, and the girl character isn't a whiny wimp.
She was certainly a lot braver than I'd have been in those sixty pages of mines and tunnels; they'd have had to cut my throat and leave me there because I'd have refused to squeeze through that final section, assuming I'd made it that far. That part of the book might have been more frightening than the fighting at the end.
The one problem I had was that I kept distracting myself by drawing parallels to The Fellowship of the Ring (the Mines of Moria and Lothlorien, in particular), but that wasn't a huge issue.
I bought my copy in Boston, along with a bunch of other used books that have been living in boxes for years, unread. I always wondered why it has Darth Vader on the cover. (My version is shown in the bottom row on this page.) Reading the book only partially helped explain that (that's not how I pictured the character at all); I wonder if the edition's being printed in 1978 might be part of the answer.