Dope accessing superlatively exceptional region under threat (10)
I believe the answer is:
rainforest
'region under threat' is the definition.
(the Amazon Rainforest is endangered)
'dope accessing superlatively exceptional' is the wordplay.
'dope' becomes 'info' (I've seen this before).
'accessing' indicates putting letters inside (inserted letters gain access).
'superlatively exceptional' becomes 'rarest' (the most rare).
'info' placed inside 'rarest' is 'RAINFOREST'.
(Other definitions for rainforest that I've seen before include "has lots of tropical trees" , "tropical environment" , "Luxuriant tropical woodland" , "high-growth area" , "area of the Amazon?" .)