Iron Keep & Belfry Sol

Start from the Threshold Bridge bonfire. Iron Keep has treasures that are positioned on lava or molten rocks. You won't be able to grab the treasures without a significant boost to your fire defense. Leave those treasures alone until later in the game when you have Flash Sweat.

26. Lower Iron Keep, Dark Souls II: SotFS

Defeat the Alonne Knight on the bridge as quickly as possible while not crossing over to the other side of the bridge where two iron doors are located. Two NPC red phantoms would invade you, one at a time, near those doors. Defeat the Alonne Knight, approach the iron doors but don't open it, wait a while for an NPC red phantom to invade, and dispatch of the phantom. The first NPC red phantom to invade is either Fencer Sharron (a melee fighter) or Armorer Dennis (a magic caster). Be ready with a shield that has as high magic defense as possible and equip the Magic Quartz Ring+1. Defeat one NPC red phantom, rest at the Threshold Bridge bonfire, dispatch of the Alonne Knight on the bridge again, approach the iron doors, and wait for the second NPC red phantom to invade. After defeating both red phantoms, open the iron doors and deal with the enemies inside.

Magerold of Lanafir sits in a corner to the far right after you open the iron doors. Dispatch of the nearby Alonne Knights first before you exhaust his dialogue. Purchase a Fragrant Branch of Yore for 7,500 souls from him. He also sells the Jester armour set, which is useful for farming purposes. The Jester's Cap raises your item discovery, while the Jester's Gloves increase the number of souls you absorb from defeated enemies. Spend at least 10,000 souls in his shop, exhaust his dialogue, and you would be gifted with the Covetous Gold Serpent Ring+1, which raises your item discovery. The effect of the ring stacks with the Jester's Cap, the Watchdragon Parma, and the Prisoner's Tatter, just as the effect of the Jester's Gloves stack with the Covetous Silver Serpent Ring+1 that you received from Melentia.

Notable loots:

• Life Ring+1. Within an iron chest near an Alonne Knight Captain. Equip the ring to boost your HP.
• Ring of Blades+1. Dropped by the Pursuer. Defeat the Smelter Demon and rest at the Ironhearth Hall bonfire. Return to the boss arena and the Pursuer would spawn. Defeat the Pursuer to obtain the Ring of Blades+1, which boosts your physical attacks. Buff your weapon with Aromatic Ooze or Charcoal Pine Resin when you fight the Pursuer.
• Covetous Gold Serpent Ring. Found on a corpse on a cauldron filled with lava. The item can only be collected by dropping down from above. You don't need to grab this ring since you should already have the +1 version from Magerold.
• Iron Key. Above the Eygil's Idol bonfire is a lever, pulling which would turn off the fire-breathing statues. In front of the very first fire-breathing statue at Iron Keep is the Iron Key. You need the Iron Key to access an area at the Forest of Fallen Giants, which contains another key that allows you access to the Crown of the Old Iron King DLC.

Smelter Demon

This boss can be poisoned. Buff your weapon with magic, lightning, or dark. During the second phase, the abdomen of the boss becomes a cauldron of fire. Being very close to the boss would result in the fire doing chip damage to your HP. The Rapier is recommended because you don't have to be very close to the boss for an attack to connect. Lucatiel is available to be summoned for the fight against the Smelter Demon. By now, you should have already summoned her for three different boss fights and she survived all those fights. There is no need to summon Lucatiel to help you against the Smelter Demon. Her quest line is nearly complete by now.

27. Upper Iron Keep, Dark Souls II: SotFS

Like Belfry Luna, Belfry Sol is an invasion hot spot. Play offline in case you don't want to be invaded by other players. Summon Drifter Swordsman Aidel to help you clear the area. Before fighting the Old Iron King, ensure you have purchased all Brightbugs from Melentia. After defeating the Old Iron King, Melentia would restock her inventory of Brightbugs and any Brightbugs you haven't purchased would be lost forever.

Old Iron King

28. Old Iron King, Dark Souls II: SotFS

This boss is weak against lightning. Aromatic Ooze and Dark Pine Resin are also effective, but Charcoal Pine Resin should be a last resort because the boss has immense fire defense. Stack as high fire defense as you can or consume a Small Orange Burr.

Defeat the Old Iron King and light a Primal Bonfire. The Alonne Knights and other enemies at Iron Keep are a good source of souls. After defeating the Old Iron King and before moving on to a different area of the game, consider farming enemies at Iron Keep so you can level up a few times.