Tower in Paris is quite a sight they say (6)
I believe the answer is:
eyeful
'sight they say' is the definition.
'eyeful' can be an answer for 'sight' (I have seen 'Attractive sight' mean 'eyeful' so perhaps 'sight' could also mean 'eyeful'). I'm unsure of the 'they say' bit.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for eyeful that I've seen before include "Gorgeous sight" , "Something worth looking at" , "great sight" , "Fascinating sight" , "As much as can be taken in by a look" .)