A party opening up a temple (6)
I believe the answer is:
pagoda
'a temple' is the definition.
(pagoda is a kind of temple)
'a party opening up' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'opening' becomes 'gap' (gap is a kind of opening**).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'a'+'do'+'gap'='adogap'
'adogap' written backwards gives 'PAGODA'.
(Other definitions for pagoda that I've seen before include "Hindu temple shaped like pyramid" , "Buddhist memorial building" , "Eastern building" , "Many-tiered building" , "Eastern tiered tower" .)