Arrived by luck at Arthur's Seat (7)
I believe the answer is:
camelot
'arthur's seat' is the definition.
(court of King Arthur)
'arrived by luck' is the wordplay.
'arrived' becomes 'came' (coming is a kind of arriving).
'by' is a charade indicator (letters next to each other).
'luck' becomes 'lot' ('lot' can be a synonym of 'luck').
'came'+'lot'='CAMELOT'
'at' acts as a link.
(Other definitions for camelot that I've seen before include "mythical place" , "Musical about King Arthur" , "legendary town" , "Location of King Arthur's court" , "King Arthur's court - or JFK's" .)