Head down the Iron Passage on your path to fight the Smelter Demon again.
From the Foyer bonfire, use the Tower Key and unlock the door on the far side near the lift. Head down the stairs and go right at the bottom, where you'll come across two Twilight Herbs. get in the lift on the other side of the platform and go down and through the tunnel to the entrance of the Iron Passage.
Light the bonfire and drop to the room below. There are two markings here where you can summon helpers to the fight. Go through the hallway and from the next room you find a corridor lined with cells on both sides and a gate at the end. The cells contain lots of enemies.
If you're not up for a fight, pull the lever in the center of the room and run quickly to the gate and pass through it. It only stays open for a short time and it also opens all the cell doors so don't hang around.
Pull the lever in the middle of the next room which will activate a fireball trap and unlock cells containing four Axe Demons. Move to the side and you'll avoid the fireballs and prepare to fight two Axe Demons. once all enemies are killed you'll find seven Large Titanite Shards in the third cell on the right.
Go back in the the room with the lever and through the passage at the side where you can drop below and fight two Axe Demons and two Hollow Mages. You'll need to use ranged attacks for the Mages.
Once they're killed drop down to the small alcove at the end but not all the way to the next corridor. Used ranged attacks to kill the Axe Demon below you then you can drop down to the corridor. Ahead you're going to have to fight three Axe Demons, two Possessed Armors, one Fume Sorcerer and one Hollow Mage. You'll need to use ranged attacks on all of them.
You can sprint through the room but you'll still need to at least take down the Axe Demons and we'd advise killing the Hollow Mage with ranged attacks too. In the next room are Giant Club Demons with flames from their bodies, two Axe Demons, two Hollow Mages and a Possessed Armor.
After the first gate opens
Before the gate closes drop into the gate at the end and fight the Hollow Mage. His slow magic attacks aren't a big problem. From the fireball trap you'll be able to see two Mages and some Axe Demons, none of which can reach you from here, so take them down with ranged attacks.
Head into that room and you'll find two Crimson Waters on the left. Go back to the fireball trap and through the passage on the opposite side.
A Fume Sorcerer will attack as soon as you enter here, so take it down and decide which of the two paths you're going to take. When you pull the lever the cells and gates in the next corridor open but again you need to run quickly to the gate before it closes.
If you decide to go through the side passage you'll end up on the bottom floor of the next room on a raised platform with the two Possessed Armors ahead of you, a Hollow Mage on the upper platform, and two Axe Demons on the ground floor. In the corner a third Axe Demon stands in front of one of the exits into the last room.
Kill the two Possessed Armors and go up the other exit straight ahead and to the right. There are two Wilted Dusk Herbs here. This exit is only accessible from the raised ledge.
If you drop down to the ground you will have to use the exit blocked by the Axe Demon. No matter which exit you take, both lead to the same location in the final room before the Smelter Demon.
The final room has one Possessed Armor on the ledge above, two Giant Club Demons, and two Hollow Mages on the ground floor. The Giant Club Demons stand in front of the mist door and the final boss. If you have helpers still with you, let them distract the enemies, then head to the mist door to take on the Smelter Demon. There's also a Dried Root on the floor near the closest Hollow Mage if you're feeling brave.
The second gate
Pull the lever, run to the gate and drop to the room below, You'll be face-to-face a Hollow Mage which you should totally kill. Two Possessed Armors and two Axe Demons await down below, but
there's nothing for you in the upper area that you have access to. Go down the path to the right.
Go around the next corner but don't go into the room. There is a Possessed Armor on the same height level you're on. Kill it with a ranged attack from the corridor and you can use the wall for cover. Below there are two Giant Club Demons and two Hollow Mages. Kill them with ranged attacks and dodge the return fire from the Mages.
At the end of the path are three Cracked Red Eye Orbs and three Old Growth Balms. Take them and drop down below to find a Dried Root. Now it's time for your fight with the Smelter Demon.