Suggest visiting quiet flat (6)
I believe the answer is:
smooth
'flat' is the definition.
(thesaurus)
'suggest visiting quiet' is the wordplay.
'suggest' becomes 'moot' (I can't explain this - if you can you should give a lot more credence to this answer).
'visiting' means one lot of letters goes inside another.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'moot' placed into 'sh' is 'SMOOTH'.
Can you help me to learn more?
(Other definitions for smooth that I've seen before include "Still" , "Unruffled" , "Regular - without problems" , "Without lumps" , "Level, not lumpy" .)