The most common and most likely answer to this crossword clue is the 12 letter word STRATOSPHERE
I've seen this crossword clue in The Guardian
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More clues leading to the result STRATOSPHERE
- Elevated position in Mad Hatter’s prose
- Eight Miles High? One’s in this guitar shop, playing before …
- Nuts stop and stare endlessly at this place, somewhere in the sky
- Spotters hear cuckoo in part of the sky
- These parrots must suffer, reaching such height
- Travelling to stars: reduced pressure in this place?
- Region organised sports at my place
- He rates sport wrongly — it’s way above us!
- Somewhere far away protester has messed up
Buddy explains!

The straight part
We know that "Eight Miles High?/ One’s in this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case eight miles high?/ one’s in this = stratosphere.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does STRATOSPHERE mean?
STRATOSPHERE noun- Collectively, those layers of the Earth’s crust which primarily comprise stratified deposits.
- The region of the uppermost atmosphere where temperature increases along with the altitude due to the absorption of solar ultraviolet radiation by ozone. The stratosphere extends from the tropopause (10–15 kilometers) to approximately 50 kilometers, where it is succeeded by the mesosphere.