Complex sentence: The castle and its dungeons were the central location for his campaign which he described in a 1975 article titled, "Adventure at Greyhawk Castle", for a Diplomacy fanzine named "El Conquistador".
Split into simpler sentences: The castle and its dungeons were the central location for his campaign at the time. He described these in a 1975 article entitled "Adventure at Greyhawk Castle" in the Diplomacy fanzine "El Conquistador".