Complex sentence: Situated on the former Polo Park Racetrack, the Polo Park Mall opened on August 20,1959 and was the first enclosed shopping mall in Winnipeg when a roof was added in 1963.
Split into simpler sentences: Situated on the former Polo Park Racetrack, the Polo Park Mall was built in 1959. It was the first enclosed shopping mall in Winnipeg when a roof was added in 1963.