Domed recess cathedral ultimately abandoned by mistake (4)
I believe the answer is:
apse
'domed recess' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for apse that I've seen before include "Part of a church with the altar" , "Semicircular recess in church" , "Domed section of a church" , "Offshoot from the choir, nave or aisle in a church" , "Semicircular end of a church, behind the altar" .)