From the Blighttown swamp bonfire, look for a large hill off in the distance to your right. This is your destination. There are barbarians around it who will throw massive boulders at you which cannot be blocked, so unless you’re feeling brave, simply dash into the opening found halfway up the hill.
Simply run through this tunnel, making sure not to attack the Egg Carriers. These creatures are not initially hostile, and the maggots that are released upon their death can be extremely inconvenient.
If you are in human form and have already defeated the Black Phantom Maneater Mildred, her summon sign will be in front of the fog door. We suggest using it.
Equip armor and a shield that has high fire resistance. The Dragon Crest Shield found in the previous optional section works well, as does the Stone Armor Set, which is found in a chest in Darkroot Garden (next to the tower across the bridge from Alvina’s tower).
Try to avoid Quelaag at first so that she goes after Maneater Mildred. This allows you to get behind the boss, put your weapon in both hands, and hack away.
Quelaag’s firesword is extremely deadly, so we suggest you read her swings and attempt to roll away from them as opposed to blocking them. The most damaging firesword attacks are her stabs, which are slow and telegraphed. Stabs come at the end of a three-hit combo or as a singular attack. Rolling to either side at the very last moment (her stabs track) will keep you out of harms way.
The goal is to get around the side or rear of Quelaag an attack using your weapon. When she pets her spider’s head, that means lava vomit is coming, but it also means you have plenty of time to maneuver around back. If you stay too close for too long, Quelaag will release a deadly wide-radius attack. When you see her human form bend down and her spider form curl up, back away!
If you run too far from Quelaag, she’ll perform a leaping attack and hurl lava at you. This is hard to avoid (usually rolling forward underneath her as she flies towards you works) so we don’t suggest you stray too far.
Quelaag will drop the Soul of Quelaag (DO NOT CONSUME THIS OR ANY BOSS SOUL) and Twin Humanities. Continue to the other side of her domain, up the steps, and into the bell tower. Pull the lever to ring the second bell! This opens up the gate to Sen’s Fortress – but first let’s take care of some local business.
Descend the nearby steps (or fall through the hole in the middle of the room). There are two directions you can go from this lower level: left, through the broken brick wall, leads to a bonfire and the Demon Ruins. Right, through an illusory wall, also leads to a bonfire and Eingyi, an NPC (not an enemy!). Go that way. Talk to Eingyi and answer “yes.” He will then move away and you can light the nearby bonfire.
You may now also speak to Quelaag’s Sister. She is the leader of the Chaos Servant covenant, so join up if you wish. If you do, you’ll be rewarded with Pyromancy: Great Chaos Fireball. If you’re pursuing Pyromancy, this is a must-have. Quelaag’s Sister is also a Fire Keeper, so you can use the Fire Keeper’s Soul you picked up in Blighttown to reinforce your flasks.
Eingyi can reinforce your Pyromancy Flame and initially sell you the Chaos Servant Roster. If you become infected by eggs, he will show a liking to you and sell you Egg Vermifuges (which cure egg infections), Pyromancy: Toxic Mist, and Pyromancy: Poison Mist. To pick up an egg infection, kill an Egg Carrier (found in Quelaag’s Domain or the Demon Ruins) and let one of the maggots hit you with their blood spray attack (more than once). Alternatively, agitate an egg carrier, who will then latch on to you.
If successfully infected, you character will start scratching their head when standing still. Soon after, your head will transform into a hideous egg formation. This can only be cured by using an Egg Vermifuge.
At this point in the game, Sen’s Fortress is your next objective. However, you should be strong enough to tackle several optional areas. We’re going to do a bit of exploring right now, but if you just prefer to get on with things, skip ahead to Sen’s Fortress.