Monument left with blemish (8)
I believe the answer is:
landmark
'monument' is the definition.
(I've seen this before)
'left with blemish' is the wordplay.
'left' becomes 'l' (common abbreviation).
'with' becomes 'and' (I've seen this before).
'blemish' becomes 'mark' (mark is a kind of blemish**).
'l'+'and'+'mark'='LANDMARK'
(Other definitions for landmark that I've seen before include "Durham Cathedral, say" , "Damn lark (anag.)" , "of great significance" , "Significant feature or event" , "Notable geographical feature" .)