Transform a marsh into a hermitage (6)
I believe the answer is:
ashram
'a hermitage' is the definition.
(I have seen 'Indian hermitage ' mean 'ashram' so perhaps 'hermitage' could also mean 'ashram')
'transform a marsh' is the wordplay.
'transform' indicates an anagram.
'a'+'marsh'='amarsh'
'amarsh' is an anagram of 'ASHRAM'.
'into' is the link.
(Other definitions for ashram that I've seen before include "religious community" , "Hindu place of retreat" , "Retreat -- a marsh (anag)" , "holy man's retreat" , "Place of religious retreat for Hindus" .)