Firstly, a very interesting architect redesigned Yucatan bird sanctuary (6)
I believe the answer is:
aviary
'bird sanctuary' is the definition.
(I know that Aviary is a bird sanctuary)
'firstly a very interesting architect redesigned yucatan' is the wordplay.
'firstly' indicates taking the first letters.
'redesigned' indicates an anagram.
'yucatan' becomes 'ary' (I am not sure about this - if you are sure you should believe this answer much more).
The first letters of 'very interesting architect' is 'via'.
'via' with letters rearranged gives 'avi'.
'avi'+'ary'='AVIARY'
Can you help me to learn more?
(Other definitions for aviary that I've seen before include "Large enclosure for birds" , "cages perhaps" , "restricted flights here" , "House for birds" , "Large cage for birds" .)