In Venice strolling is most agreeable (6)
I believe the answer is:
nicest
'most agreeable' is the definition.
(I've seen this before)
'in venice strolling is' is the wordplay.
'in' says the answer is hidden in the clue.
'NICEST' can be found hidden inside 'venice strolling is'.
(Other definitions for nicest that I've seen before include "Best" , "I scent in the most pleasant way" , "Most attractive" , "Most pleasant or fine" , "most appetising" .)