Notre-Dame is an area of Dracula's Castle. Its Mirrors of Life sit in the Notre-Dame Undercroft, the West Triforium and the East Gallery, and the Ferryman's Wharf is in the East Triforium.
Arthur is fought in the Chapel, with the East Gallery as the closest Mirror of Life, and beating him gives The Brittle King, the Stained-Glass Shield and Excalibur. Death waits in the Choir, also nearest the East Gallery mirror, and drops The Shadow and Soul Harvest. Double Jump is picked up in the Choir along with the Arcana of Death. Doppelganger is fought in the Gallery of the Four Virtues, nearest the West Triforium, and gives The Self and Absolution. Joan is fought in the Courage of Gabriel, with the West Triforium as the nearest Mirror of Life.
Chests hold Witch's Brew in the Transept, Soul Fragment in the Nave, Eldritch Talisman in the East Gallery, Beelzebub's Seal in the Chapel of Patience and Infernal Medallion in the Reliquary. For weapons, look for Arondight and Lancelot's Shield in the Tower Entrance, Joyeuse on the Path of the Penitent and War and Famine in the Great Organ Room. You can pick up 3 Brave and 3 Wise Heart Fragments, plus 4 ATK and 3 DEF books, 2 of the ATK books inside Secret Areas in the Tomb of the Chevaliers. There are 19 XP statues worth 300 XP each and 31 Secret Areas.
The Narthex leads out to the Main Hall. Sypha is in the Gallery of the Four Virtues and Trevor in the Deacon's Quarter. Clues for The Shadow include Melody Sheets in La Flèche, the Great Organ Room and the Sealed Scriptorium. Expect skeleton archers, gargoyles, harpies and minotaurs.