Have you tried the unique outdoor maps like the Forest ones, or Croatoa, or Eden?
I believe it's Forest 02 that has a more open feel and the chirping birds and waterfall background noises. Despite the "forest" in the name it's more of a rocky meadow with scattered trees and a shoreline. It's the most "peaceful" map I've found so far.
You could also experiment with the various Croatoa spirit world maps; the golden haze could be part of the otherworldly setting.
Miuramir, Windchime, Sariel the Golden, Scarlet Antinomist...
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Could anyone suggest a map that would emulate the Elysian Fields? I have bought all the extra maps already.