There is a plenty of places worth seeing in Sevilla:
The cathedral (Catedral de Santa María de la Sede de Sevilla), in particular its bell tower, La Giralda, originally built as a minaret of the Seville’s impressive mosque, as well as the tomb of Christopher Columbus. More: http://www.catedraldesevilla.es/
Metropol Parasol (Las Setas de Sevilla), allegedly the largest wooden structure in the world. According to some estimates it cost EUR 100 m to construct, due to delays and changes in design. More: http://setasdesevilla.com/
Real Alcázar – a complex of royal palaces surrounded by impressive gardens. More: http://www.alcazarsevilla.org/. It was used as a filming location of the Water Gardens of Dorne in the Game of Thrones series (more here).
The district of Macarena, in particular Basílica de la Macarena, with the famous statue of María Santísima de la Esperanza Macarena (http://www.hermandaddelamacarena.es/)