Atmosphere in Colorado metropolis (5)
I believe the answer is:
cairo
'metropolis' is the definition.
The answer and definition can be both locations as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'atmosphere in colorado' is the wordplay.
'atmosphere' becomes 'air' (synonyms).
'in' means one lot of letters goes inside another.
'colorado' becomes 'CO' (abbreviation).
'air' placed into 'co' is 'CAIRO'.
Can you help me to learn more?
(Other definitions for cairo that I've seen before include "Egypt's capital" , "Al Qahira" , "North African capital" , "African city" , "Capital of Egypt" .)