Praise mysterious ancient land (6)
I believe the answer is:
persia
'ancient land' is the definition.
'praise mysterious' is the wordplay.
'mysterious' is an anagram indicator.
'praise' anagrammed gives 'PERSIA'.
(Other definitions for persia that I've seen before include "Iran, formerly" , "Old Iran" , "Former name of Iran" , "Old name for country at 25 Across" , "Old land" .)