Scene of promontory by the outskirts of Lagos (9)
I believe the answer is:
landscape
'scene' is the definition.
(I've seen this before)
'promontory by the outskirts of lagos' is the wordplay.
'promontory' becomes 'cape' (I've seen this before).
'by' says to put letters next to each other.
'the outskirts of lagos' becomes 'lands' (I can't explain this - if you can you should believe this answer much more).
'cape' after 'lands' is 'LANDSCAPE'.
'of' acts as a link.
(Other definitions for landscape that I've seen before include "Type of painting" , "The visible features of an area" , "Piece of inland scenery" , "Countryside painting" , "(Painting of) scenery" .)