Valuable park in very holy surroundings (8)
I believe the answer is:
precious
'valuable' is the definition.
(similar in meaning)
'park in very holy surroundings' is the wordplay.
'park' becomes 'rec' (short for recreation ground).
'in' indicates putting letters inside.
'very holy surroundings' becomes 'pious' (I can't justify this - if you can you should give a lot more credence to this answer).
'rec' put into 'pious' is 'PRECIOUS'.
Can you help me to learn more?
(Other definitions for precious that I've seen before include "Having great value" , "as good as gold" , "Much loved" , "highly esteemed" , "Of high worth or cost" .)