This opera may be something to see in a German cave! (3,10)
I believe the answer is:
die fledermaus
'this opera may' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'something to see in a german cave' is the wordplay.
I cannot quite see how this works, but
'something' could be 'er' (I've seen this in other clues) and 'er' is found in the answer.
'a' is within the answer.
'german' could be 'd' (abbreviation for Deutschland ie Germany) and 'd' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'be' is the link.
Can you help me to learn more?
(Other definitions for die fledermaus that I've seen before include "Johann Strauss operetta (The Bat)" , "Strauss work" , "Musical drama" .)