To which ruined tower cardinal is admitted? (7)
I believe the answer is:
whereto
'to which' is the definition.
(synonyms)
'ruined tower cardinal is admitted?' is the wordplay.
'ruined' indicates anagramming the letters.
'cardinal' becomes 'he' (I've seen this in other clues).
'is admitted?' means one lot of letters goes inside another (inserted letters are admitted in).
'tower' with letters rearranged gives 'wreto'.
'wreto' placed around 'he' is 'WHERETO'.
(Other definitions for whereto that I've seen before include "To which (archaic)" , "Towards which place" .)