The last item is the Holy Sword. Due to a bug, you can enter this area by getting the Nericon garden key from merchant Blake in Ars Magicana or the chest key (the sapphire one) from the alchemist Walker in Ars. Another possibility is following the game plot and entering the castle. You're thrown out, kidnapped and are in Iona's/Elona's dungeon. If you find the exit, you'll see it's this cemetary and the grave leads to the level where you find the sword..