There is a blacksmith on the second level of the citadel, in the far north east. You can listen to a conversation he has with an imp when you approach, but can not get the key to the door until after entering Samuel's lair.
The book about poisonous creatures is on the level you started out on, in the left spider cell of the arena, where you jumped down a pit and the DK criticized you for missing the hay stack. If you return to the first level of the citadel where you came in (and got the disguise citadel armour), and then take the stairs, you will be on the level with the arena.
