Huge region needing no introduction, part of SW Europe (6)
I believe the answer is:
iberia
'part of sw europe' is the definition.
(peninsula encompassing Spain and Portugal)
'huge region needing no introduction' is the wordplay.
'huge region' becomes 'siberia' (large region of Russia).
'needing no introduction' means to remove the first letter.
'siberia' with its initial letter removed is 'IBERIA'.
(Other definitions for iberia that I've seen before include "Peninsula that was Roman province" , "old part of Europe" , "Spanish/Portuguese peninsula" , "Spain and Portugal - airline" , "Great European peninsula containing Spain and Portugal" .)