Noted visitor to the underworld (7)
I believe the answer is:
orpheus
This clue might be a double definition.
'noted visitor' is the first definition.
The definition suggests a singular noun which matches the answer.
'the underworld' is the second definition.
Both the definition and answer are singular nouns.
Maybe you can see an association between them that I don't see?
'to' is the link.
Can you help me to learn more?
(Other definitions for orpheus that I've seen before include "In Greek myth, he went into the Underworld to rescue Eurydice from the dead" , "In Greek myth he sought his wife Eurydice in the Underworld" , "Underworld figure" , "Thracian poet" , "classical musician" .)