The characters in the opera The Visitors are escaping the Black Death by sheltering in a villa outside what city
The Visitors (opera):  The libretto (like those for "Pagliacci" and "Ariadne auf Naxos") uses the device of a play within a play to reflect and intensify the relationships between the protagonists, who in this case are loosely based on characters in "The Decameron".
i don't know