Fantastic place for a fire, we hear (5)
I believe the answer is:
great
'fantastic' is the definition.
(fantastic can mean great or excellent)
'place for a fire we hear' is the wordplay.
'place for a fire' becomes 'grate' (recess for a fireplace).
'we hear' indicates a 'sounds like' (homophone) clue.
'grate' is a homophone of 'GREAT'.
(Other definitions for great that I've seen before include "Very good or very big" , "Huge or outstanding" , "Wonderful" , "Of major significance - very good" , "Of considerable size" .)