Complex sentence: The Castle of San Jorge was a medieval fortress built on the west bank of the Guadalquivir river, inside the city of Seville (Spain), which was also used as a headquarters and prison for the Spanish Inquisition.
Split into simpler sentences: The Castle of San Jorge is a medieval fortress built on the west bank of the Guadalquivir river located in the city of Seville (Spain). It was also used as a headquarter and prison for the Spanish Inquisition.