"Secondary Lore" is a collection of popcultural worlds of well-developed fantasy fiction, that draws from or intertwines with the lore or mood of the British isles.
Watership Down (1972)
Book | Fantastic read; not only a 2ndary Lore of the landscape, but also an intense evocation of the natural world, a spiritual text, a classic of children's weird, and linked to the most iconic haunted generation film of all time. I love this book so much.
The Silmarillion (1977)
Book | For completionists only.
Lord of the Rings (1955)
Book | The one, the only. Look, you don't have to read it. You're either a Tolkien person or you're not. For spiritual purposes, this isn't my top recommendation (on the grounds of its length and comparative inaccessibility); the Hobbit, Smith of Wootton Major, and On Fairy Stories are better choices if the thought of reading this one makes you hrmmm. But I am a Tolkien person, whole-heartedly, and it's marvellous. The template of what our imaginative play can be. It will not shock you to discover that I am a Tom Bombadil person (Chapters 6, 7, 8 in Fellowship)
The Book of Lost Tales: 1 (1982)
Book | I find Tolkien's unfinished and fragmentary works far more charming than his full ones: it's either the Hobbit for me, or some scrap on the back of an exam-paper he dashed off with a smudgy pencil. I suppose this was an early indication of my attraction to Landweird, for it is not clear if these ideas are no longer in the mythos or merely abandoned and never polished up - and I find that really compelling, far more so than the coherent Silmarillion. This book has some very nice imagery of the Cottage of Lost Play as a framing device for an early draft of the first chapters of the Silmarillion narrative. The latter is less interesting to me than the unfixed strangeness of the Cottage itself; but it is not generally recommended. Its niche Tolkien.
The Hobbit (1937)
Book | If you only read one Tolkien, make it this. Probably the best thing he wrote, and accessible to all.