shadowland

[shad-oh-land]

noun

a land or region of shadows, phantoms, unrealities, or uncertainties: the shadowland of imagination.

Origin of shadowland

First recorded in 1815–25; shadow + -land

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

She knew that she was just a woman, after all, and he was a man, and the Dukedom had gone into shadowland.
The Career of Katherine Bush
Elinor Glyn
We will follow soon the others who have gone to the Shadowland.
John Ermine of the Yellowstone
Frederic Remington
Reprinted from Shadowland, a magazine, by permission of the publishers and the author.
Fifty Contemporary One-Act Plays
Various
You see him only when the sunlight is on the face; you don't see him when he is in shadowland.
Think
Col. Wm. C. Hunter
Not a Doomsman set out upon his long journey to the shadowland but that a Southron was forced to bear him company.
The Doomsman
Van Tassel Sutphen

also shadow-land, 1821, "abode of ghosts and spirits," from shadow (n.) + land (n.). From 1923 as "indeterminate place."