The fight takes place in Chamber of Oracles. If this is not your first Maat fight, you must walk to the BC; Maat will not teleport you. To get to Chamber of Oracles, you'll have to pass a couple weight switches in Quicksand Caves, so if you're not a Galka, you'll need someone to help you open them [works with 1 Galka, 2 Hume/Elvaan/Mithra, 3 Tarutaru, or Loadstone].