Lulu (opera)
The shape of the whole opera is often said to be like a mirror – Lulu's popularity in the first act is mirrored by the poverty she lives in during Act III.  Also, Lulu's husbands in Act I are played by the same singers as her clients in Act III.  In the middle of the opera is the movie.  Even some of the music is a palindrome (it reads the same forwards as backwards). This can be seen at the very middle of the Act II movie Interlude, when a piano plays a rising pattern of notes, which then reverses direction and falls.