Complex sentence: It was open for one year until, in the fall of 1968, a fire completely destroyed the school building, leaving only the original gymnasium (which remains the only building standing on the campus from the original school structure).
Split into simpler sentences: It was open for one year until tragedy struck in the fall of 1968. A fire completely destroyed the school building, leaving only the original gymnasium (which remains the only building standing on the campus from the original school structure).