Capitol feature (7)
I believe the answer is:
rotunda
'capitol feature' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rotunda that I've seen before include "domed hall" , "Round domed room" , "Circular building with a dome" , "Do a turn (anag) -- circular domed building" , "Round building or hall" .)