Nobel is known to have been impressed by this monument (7)
I believe the answer is:
obelisk
'been impressed by this monument' is the definition.
'obelisk' can be an answer for 'monument' (type of monument or landmark). I am unsure of the remainder of the definition.
'nobel is known to have' is the wordplay.
'to have' indicates the answer is hidden within the clue.
'OBELISK' can be found hidden inside 'nobel is known'.
Can you help me to learn more?
(Other definitions for obelisk that I've seen before include "Tapering, rectangular stone column" , "Cleopatra's Needle, perhaps?" , "Tapering pillar erected as monument" , "Needle-like column" , "Tapering monumental pillar" .)