... passing fancy area in Finland on vacation (3)
I believe the answer is:
fad
'passing fancy' is the definition.
(I've seen this before)
'area in finland on vacation' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'in' is an insertion indicator.
'on vacation' says to hollow out the word (remove centre letters).
'finland' with its centre taken out is 'fd'.
'a' placed into 'fd' is 'FAD'.
(Other definitions for fad that I've seen before include "A craze, usually passing" , "Caprice" , "'Craze, all the rage (3)'" , "A passing fashion or craze" , "A passing fancy or fashion" .)