Somewhat dry quarry walls (6)
I believe the answer is:
pretty
'somewhat' is the definition.
(I've seen this before)
'dry quarry walls' is the wordplay.
'dry' becomes 'tt' (short for teetotal - no alcohol).
'quarry' becomes 'prey' (synonyms).
'walls' is an insertion indicator (to 'wall' can mean to contain).
'tt' going inside 'prey' is 'PRETTY'.
(Other definitions for pretty that I've seen before include "Pleasing on the eye" , "Attractive - quite" , "pulchritudinous" , "Pleasing to look at" , "sweet" .)