Complex sentence: The Napa Valley Opera House is a theatre in Napa, California, USA which opened on February 13,1880 with a production of Gilbert and Sullivan's "HMS Pinafore".
Split into simpler sentences: The Napa Valley Opera House is a theatre in Napa, California, USA. It made its debut on February 13,1880 with a production of Gilbert and Sullivan's "HMS Pinafore".