Make a mistake, going topless in church recess (4)
I believe the answer is:
apse
'church recess' is the definition.
(part of a church)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for apse that I've seen before include "Niche in church" , "Large recess in church" , "where praetor sat" , "Where you could find a magistrate's chair" , "In sacred space" .)