Miracle realm built around Midhaven (6)
I believe the answer is:
marvel
'miracle' is the definition.
(thesaurus)
'realm built around midhaven' is the wordplay.
'built' indicates anagramming the letters.
'around' indicates putting letters inside.
'midhaven' becomes 'v' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'realm' anagrammed gives 'marel'.
'marel' placed around 'v' is 'MARVEL'.
Can you help me to learn more?
(Other definitions for marvel that I've seen before include "Wonder, be astonished" , "Be filled with wonder - something wondrous" , "Wonderful person or thing" , "Express astonishment" , "Be filled with surprise or wonder" .)