Puzzle touring Aintree bars (11)
I believe the answer is:
brainteaser
'puzzle' is the definition.
(I've seen this before)
'touring aintree bars' is the wordplay.
'touring' indicates an anagram (letters move or tour around).
'aintree'+'bars'='aintreebars'
'aintreebars' is an anagram of 'BRAINTEASER'.
(Other definitions for brainteaser that I've seen before include "It might be difficult" , "Puzzle" , "difficult exercise" , "Puzzling thing" .)