Climbing mountains outside of Yorkshire, 500 spread out (7)
I believe the answer is:
splayed
'spread out' is the definition.
(I've seen this before)
'climbing mountains outside of yorkshire 500' is the wordplay.
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'mountains' becomes 'alps' (European mountain range).
'outside of' suggests removing the centre.
'500' becomes 'D' (Roman numeral for 500).
'yorkshire' with its centre taken out is 'ye'.
'alps' backwards is 'spla'.
'spla'+'ye'+'d'='SPLAYED'
(Other definitions for splayed that I've seen before include "Turned out" , "with legs apart" , "Spread apart" .)