Greek poet’s house overlooking sea at Boulogne (5)
I believe the answer is:
homer
'greek poet's' is the definition.
(I've seen this before)
'house overlooking sea at boulogne' is the subsidiary indication.
'house' becomes 'home' (homing is a kind of housing).
'overlooking sea at boulogne' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'home'+'r'='homer'
(Other definitions for homer that I've seen before include "Trained pigeon" , "successful run in America?" , "Measure < of poet's" , "Pigeon; classic writer" , "trained to get back to house" .)