If you like live theater performances, book yourself a seat for a play or other stage show at Teatre Goya. Check online for prices and times.
You'll soon discover why this Downtown Barcelona arts and culture attraction is a hit with travelers. If you're looking for other things to keep you busy, Sagrada Familia, La Rambla, and Plaça de Catalunya are in this area too. They won't take you long to get to from Teatre Goya.