Complex sentence: The shopping mall adjacent to the tower, Atrium, was opened on the same date as the first modern mall in Ankara and the second in Turkey after Galleria in Istanbul, which was opened in 1987.
Split into simpler sentences: The shopping mall adjacent to the tower, Atrium, was opened on the same date. It was the first modern mall in Ankara and the second in Turkey after Galleria in Istanbul, which was opened in 1987.