Complex sentence: The Aachen Open Air Pop Festival was a rock festival held on 10-12 July 1970 in Aachen, Germany, at Hauptstadion, an equestrian stadium near the Dutch border.
Split into simpler sentences: The Aachen Open Air Pop Festival was a rock festival held on 10-12 July 1970 in Aachen, Germany. The festival took place at Hauptstadion, an equestrian stadium near the Dutch border.