What's seen in Bayreuth a lot? The Ring (4)
I believe the answer is:
halo
'ring' is the definition.
(I've seen this before)
'what's seen in bayreuth a lot? the' is the wordplay.
'what's seen in' says the answer is hidden in the clue.
'HALO' is hidden within 'bayreuth a lot the'.
(Other definitions for halo that I've seen before include "Ring of light round head" , "Aureole" , "Hagiological aura featured in Christian art" , "This indicates holiness" , "Holy ring" .)