We lie with effort about massive erection (6,5)
I believe the answer is:
eiffel tower
'massive erection' is the definition.
'we lie with effort about' is the wordplay.
'with' means one lot of letters go next to another.
'about' indicates anagramming the letters.
'we'+'lie'='welie'
'welie' after 'effort' is 'effortwelie'.
'effortwelie' with letters rearranged gives 'EIFFEL TOWER'.
(Other definitions for eiffel tower that I've seen before include "Paris landmark, constructed 1889" , "Parisian landmark, built 1889" , "Noted landmark" , "Tall structure" .)