Poem about concert hall (5)
I believe the answer is:
odeon
'concert hall' is the definition.
(I know that odeon is a type of concert hall)
'poem about' is the wordplay.
'poem' becomes 'ode' (ode is a type of poem).
'about' becomes 'on' (as in a book 'on' a certain topic).
'ode'+'on'='ODEON'
(Other definitions for odeon that I've seen before include "Ancient Greek building for music" , "Hal" , "classical theatre" , "Theatre of ancient Rome - picture house" , "Greek venue" .)