Question: what episode of game of thrones does cersei blow up the sept?
Answer: Season 6, Episode 10: "The Winds of Winter" With the help of her mad-scientist right-hand-man Qyburn, she blew up a cache of wildfire under the Great Sept of Baelor during the trial of Margaery and Loras Tyrell, killing both them and their captor in one gigantic green explosion.