So, for me, the cliche answer is Lord of the Rings.
But another book that I've always really loved, is East by Edith Pattou. It's a very simple fantasy story, but I read it when I was much younger and it's always just felt very comfy and cozy whenever I read it.
I really hope you'll enjoy it! The sequel, West is also good, though a bit weaker than East.
I don't often reread books, just because I would rather spend my reading time with a book I haven' yet read, but East is one of the few books I've made an exception for; I must have read that book four or five times by now.