La Sonnambula is a "semi-serious" opera by Vincenzo Bellini (1801-1835). It is the story of a young woman who wanders asleep into a stranger's bedroom and is consequently accused of infidelity by her fiancé. Her innocence is only proven when she sleepwalks across a dangerous mill bridge.
The role of Amina, the sleepwalker, is famously difficult, requiring a high vocal range and complicated technique.
Adelina Patti (1843-1919) was a famous bel canto soprano, described by Giuseppe Verdi as a "stupendous artist". Born in Spain of Italian parents, she grew up in New York City and made her debut at the Academy of Music as Lucia di Lammermoor.