Castle's keep is the sixth quest location in Candy Box, as well as the third and final quest to take place in the castle. It consists of several rooms, some of which are randomly chosen and may even appear twice. This quest may drop A Magical Horn and an Old Amulet which are highly useful and worth coming back to this quest for. There is a mini-boss at the end, which is the dragon.
Ghosts can be killed easily by imps, which you summon with the imp invocation scroll. Fireballs are a new enemy that can easily kill you if you are not careful. Their low health is a clue to how they are defeated or use invulnerability.
Upon reaching the end of the rooms before the dragon a roomful of chests appear which make this level grindable.
To defeat the dragon invulnerability potions are all but needed. When it runs out, use a teleport scroll to stall you. Repeat the process until you defeat the dragon. Seeds can be helpful for a further delay.