Complex sentence: The Arima Kinen (有馬記念) is a Grade I flat horse race in Japan for three-year-old and above thoroughbreds run over a distance of 2,500 metres (approximately 1 mile 4½ furlongs) at Nakayama Racecourse in late December.
Split into simpler sentences: The Arima Kinen (有馬記念) is a Grade I flat horse race in Japan open to thoroughbreds which are three-years-old or above. It is run over a distance of 2,500 metres (approximately 1 mile and 4½ furlongs) at Nakayama Racecourse, and it takes place annually in late December.