Elfland looks and feels different from our world. As Dunsany says in Chapter III, when the English man who will one day love and marry the magical princess enters that realm,
And all of a sudden he came from the gloom of the wood to the emerald glory of the Elf King's lawns. Again, we have hints of such things here. Imagine lawns of ours just emerging from night, flashing early lights from their dewdrops when all the stars have gone; bordered with flowers that just begin to appear, their gentle colours all coming back after night; untrodden by any feet except the tiniest and wildest; shut off from the wind and the world by trees in whose fronds is still darkness: picture these waiting for the birds to sing; there is almost a hint there sometimes of the glow of the lawns of Elfland; but then it passes so quickly that we can never be sure. More beautiful than aught our wonder guesses, more than our hearts have hoped, were the dewdrop lights and twilights in which these lawns glowed and shone. And we have another thing by which to hint of them, those seaweeds or sea-mosses that drape Mediterranean rocks and shine out of blue-green water for gazers from dizzy cliffs: more like sea-floors were these lawns than like any land of ours, for the air of Elfland is thus deep and blue.
It's easy to do this sort of writing trick badly. You can really only hint at describing the indescribable; Dunsany, smartly, tries to make us feel it more than see it. Douglas Adams would have done a joke, like saying in The Hitchhiker's Guide to the Galaxy how the Vogon ships preparing to destroy Earth "hung in the air in precisely the same way that bricks don't." That's valid in its own way.
Meanwhile, still, I try to picture it. And this is the best I've done so far:
I got thinking of the fires the Pacific Northwest had in 2017 and 2018, fires I still have to hope we avoid repeating this year, crisping too many of our trees and weakening the slopes they're rooted in and adding a heavy filter of ash and dust that choked our skies, causing almost-bright-but-dingy colors I rarely see when looking up. What if something like that was happening — but, good?
It's a bass-ackwards way to look at that. It's counterintuitive. It's also the best I can do to picture the unreality of the unreal place Lord Dunsany described.
Anyway: vivid, this book.