Architectural feature mapped -- I'm enthralled somewhat (8)
I believe the answer is:
pediment
'architectural feature' is the definition.
(I've seen this before)
'mapped i'm enthralled somewhat' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'PEDIMENT' can be found hidden inside 'mapped im enthralled'.
(Other definitions for pediment that I've seen before include "(Arch.) gable" , "Triangular structure on the front of a classical building" , "Triangular architectural feature" , "Triangular part of the front on a classical building" , "Classical triangular gable" .)