Sawfish, I too have been intrigued by Lovecraft's evocation of a strange, unsuspected past of this earth; and the irruption of the past into the present is a theme of several works that impress me. In Lovecraft, it's a key element of those late works
At the Mountains of Madness and, especially, "The Shadow Out of Time." It's there in Tolkien's fascinating
Notion Club Papers, where, if anywhere, there could, conceivably, be a Lovecraftian influence on Tolkien. Though I doubt that "influence" occurred, it is not preposterous to imagine C. S. Lewis -- who was, I believe, a reader of
Astounding around the time those two Lovecraft stories were published there -- telling his friend Tolkien that the magazine contained some work much better than the run of the mill and passing those issues on to Tolkien, and then Tolkien being influenced. The irruption-into-the-present theme returns in various forms in Alan Garner's novels, with
The Owl Service being my favorite example.
I got around to reading William Morris's
The Water of the Wondrous Isles for the first time a few years ago, and then reread it more recently. That one comes to mind in connection with your comments on fantasy worlds. I'm overdue for a rereading of
The Well at the World's End. Where Dunsany was a favorite of my adolescence, I now find his characteristic dream-world fantasies get little traction in my mind, Morris seems to appeal to me more than then. To my regret, I haven't got on with Kenneth Morris's
Book of the Three Dragons in a couple of relatively recent attempts at rereading, as compared with my first reading over 40 years ago.
The weird world of the Seven Dimensions in MacDonald's
Lilith is outstanding. That book has had seven readings so far (the final version). I relish the way it begins as a haunted house story and becomes something very strange indeed.
The world of death in Charles Williams's
All Hallows' Eve is eerie, at first kind of like something from a first-rate
Twilight Zone teleplay.
Must mention Prospero's island in
The Tempest -- "'full of voices'"! Sir Thomas Malory's Logres. I enjoyed wandering on the Arthurian world of
The High History of the Holy Graal some months ago. We read in passing of Perceval seeing a burning castle: that is where King Pelles’ son Joseus killed his own mother, and it is one of two burning castles that will kindle the fire that will burn up the world at last. ...But Malory is much better. The Arthurian world of
Sir Gawain and the Green Knight in Brian Stone's translation. Gulliver's landfalls. The weird world of "The Rime of the Ancient Mariner" and Coleridge's "Christabel." The dark wood of Milton's Comus masque. I've spent many good hours with Spenser's Faerie-land.
The Earthsea of Le Guin's first three books.
The Green Kingdom of Rachel Maddux's too-little-known novel.
Certain places in late works by Arthur Machen, such as "N."
The dismal ruined world of Charn in C. S. Lewis's
The Magician's Nephew, the realm between the worlds, and Narnia. Ayesha's Kor in Haggard's novel -- which seems to have been in Lewis's mind when he wrote the Narnian chronicle just named! Glome and its environs in Lewis's
Till We Have Faces are well-realized.
Tolkien's Middle-earth.
I won't roll out a bunch of remarks on real-world places that appeal to my imagination other than to mention Murray's
Copsford, which you can read about here:
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wormwoodiana.blogspot.com]