Came across endlessly accessible feature of classical temple (6)
I believe the answer is:
metope
'feature of classical temple' is the definition.
(architectural feature)
'came across endlessly accessible' is the wordplay.
'came across' becomes 'met' (to come across is to meet or encounter).
'endlessly' means to remove the last letter.
'accessible' becomes 'open' (something open can be accessed).
'open' with its final letter taken away is 'ope'.
'met'+'ope'='METOPE'
(Other definitions for metope that I've seen before include "Face" , "Generally, one's mug" , "forehead" , "Pan" .)