- When you enter, there will be a floor switch trap right in front of the entrance to the Fortress. You will also see two Serpent Soldiers in the same room. Draw their attention and lure them to the middle, then step on the switch to launch arrows in the backs of the lizards. This should kill at least one of them easily.
- After making it through the first room, you will come upon a room with a pendulum trap. While you walk across the bridge, a Serpent Mage above will fire lightning at you. You can use arrows or magic to take it out, or block with your shield (Eagle shield from Blighttown has high lightning resistance) while you walk through the traps. Also waiting for you on the other side of the bridge is a Serpent Soldier. You can either kill him or run around and past him. When he follows you he sometimes gets killed by the pendulum. Another tactic is to shoot him with an bow from a distance. He'll then walks towards you and will likely be hit by one of the pendulum traps, causing him damage or throwing him off the bridge. Standing under the bridge which the Serpent Mage is standing on will block his lightning attacks while you fight the Serpent Soldier.
Tip for pendulum traps: Adjust your camera so that you have an almost bird's eye view of whats going on. this is especially useful for the last pendulum trap with the narrow path.
- Once past the pendulum, you have two options: 1) keep going up the stairs; or 2) drop down at the end of the narrow bridge, where the last lone pendulum is. (Alternatively if you use the Fall Control spell you can also drop down before the bridge.) You should be able to survive this fall easily, but be aware that there are three Serpent Mages waiting down here. They will challenge you immediately after you fall, and they are difficult to target from the bridge above with your bow. Once you have dealt with them, there is a Prowling Demon at the far side of the room. If you're good with a bow, you can deal with him from here with no danger of counter-attack. Otherwise, follow standard Prowling Demon protocol.
- If you chose Option 2: After you drop down from the platform with the three Serpent Mages, you will see another Prowling Demon right behind you. This one will come to you if you start shooting it with a bow, but rather slowly and there are two columns you can hide behind that restrict its mobility. Be aware that this entire area is carpeted with sucking mud; bring your Rusted Iron Ring. Kill both Prowling Demons for 2 pieces of Demon Titanite in total, and pick up a Scythe and a Soul of a Brave Warrior behind the second Prowling Demon.
- Through the corridor to your left are two Prowling Demons, which are tougher then the first two. Unfortunately there's no good way to separate them and kill them individually as the corridor stops you setting up an ideal shooting gallery. Try and hug the wall directly to your left or else the second one will fire lightning at you and start inching towards you as you fight the first one (this area is best tackled later when you can kill Prowling Demons with relative ease). Dispatch them for two more pieces of Demon Titanite, then head back to the right of this area to find a small staircase and a long ladder. Climb the ladder, pick up the Soul, then hit the illusory wall to the right of the corpse to reveal another ladder. This will take you up to a rooftop on Sen's Fortress, where you will find a Giant, evidently the one who opened the gate to Sen's Fortress after you rang both the Bells. Show him your gratefulness by dispatching him (he's not too much trouble) for a nice 3000 souls and a Titanite Chunk. Now head back down the ladder and walk off the corpse with the soul. You should be right at the beginning of the first bridge with the pendulums a richer man. Keep in mind that this entire part is easier to just come back to later when you have better equipment.
- Now, head up the stairs, another set of pendulum traps await you. This one is a bit tougher, but still should be no problem. The Serpent Mage is still waiting for you if you haven't killed it, but again you can just ignore it and run through if you want. There is a break between the first two pendulums and the last two, which you can use to prepare your attack on the mage.
- As you walk into the room after the Serpent Mage, there is a chest and another floor switch that will launch arrows from the wall in front of you, so avoid it.
- Continue on and you will come upon a door leading outside, watch out because rocks will start falling and rolling down the pathway towards you. Wait for the rock to roll by, run as fast as you can up the chute until you see an opening on the left with a fog gate. Either traverse it, or try to kill the Serpent Mage throwing lightning at you just up the path. In the room behind the mage is a box with the Ring of Steel Protection. As you exit this room, drop down to your left and you will find the Shotel sword and see Siegmeyer sitting in the distance. You will need to talk to him here to continue his storyline. There are two more Serpent Soldiers in this valley with their backs turned, and are easily backstabbed and killed if you approach them quietly. This path will lead back to the hill with the rolling boulder and you can work your way back up to the next room.
- Once you enter the room, there is a hallway with another floor switch. On the other side of the hallway is a Serpent Soldier, lure him into the hall, hit the switch (watch out, this time the arrows will come from behind you, not in front of you) if you can get out of the way, the arrows will kill the lizard for you.
- After the Serpent Soldier, you will come upon a door way, watch out because you will find stones rolling down the pathway. Again, wait for the boulder to pass, but this time follow behind it. If you keep going down after the stone you will eventually see hallway on the left and a huge pit in front of you. Run inside here before another stone comes and hits you. Now, wait here and you will notice that the stones begin to fill up the giant pit, and soon one will crash through the wall. You can then run into the secret room to grab the Covetous Gold Serpent Ring. Another possible route here is going up the stairs to your right after the boulder goes past, then dropping down off the left side at the last possible opportunity to do so (i.e., just before turning right). Doing this will put you face to face with a Serpent Mage guarding a Soul of a Proud Knight, and a passage that will take you through to a room with the full Black Sorcerer set along with the spell Hush [on right] and the Slumbering Dragoncrest ring if you proceed straight ahead on the planks and drop down to the left and continue left. When collected move to middle towards pendulums and you can safely drop down to the path below at the starting point. You can then open the prison gate and get to the room where stones are being loaded. You can also do this after the stones have stopped moving, later in the level.
- In the room will be a treasure box (probably surrounded by orange warnings if playing online). The chest is a Mimic, so don't attack it unless you can defeat it. The Mimic drops a Lightning Spear. If you attempt to open it, it will attack you and most likely kill you. Instead, attack the treasure chest, it will do damage on the mini-boss. The mini-boss itself is rather easy, all attacks (except the instant-death grab) are blockable and you'll do 50-60% of your full damage on him as his armor is low. It has about 1000 HP. The Lightning Spear is a highly effective weapon for anyone below level 70 or so, and easily deals with most enemies in this area.
- You will see an elevator with blood on it in the same room. If you ride the elevator all the way to the top, you will be impaled on ceiling spikes and die if your HP is low enough. As the elevator is going up, run towards the wall (get into the elevator, turn around 180 degrees and wait for the lift to pause when it reaches the next level, you should have more than enough time), you will eventually come upon a gap in the wall you can run through into another room.
- Once you get off the elevator and continue, you will come upon the central hub room where the rocks are being loaded and launched down the tunnels. You can go down any of the tunnels at this point, but you will find a doorway beside one of the tunnel entrances that leads to the next part of the level. You can change the direction of the balls with the big lever and break a wall (right after the second pendulum trap) where you can free Big Hat Logan and collect a hero's soul if you have the Master key, otherwise you will need to locate the Cage Key found farther into the level to open them.
- As you continue you will find a small hallway with a switch in the floor, if you press it arrows will shoot out of the left side so make sure you just jump through the hallway as fast as you can, or immediately backstep and just wait for the three-arrow volley to finish and walk through.
- Once you make it through this hallway you will come upon another pendulum trap. This trap you can't go one by one, so just back up and run through as soon as the pendulums all sweep the bridge . This isn't so bad as long as you take a run up and start running not when the pendulums are completely apart, but just as they start to move apart.
- After the pendulum trap, you will come into a small area with a few hallways. On the right is a lizard, on the left another lizard guarding a large titanite shard. Up the stairs is the correct path to continue. There is a magician here on the steps. After going up the stairs, be very wary before proceeding onto the narrow bridge. There is a magician to your left and he WILL shoot you off the bridge if you're not careful. Wait on one side and shoot him down with arrows or magic, or just take the hits as you cross if you have some poise or the Wolf Ring equipped.
- You will come upon another pendulum trap after going up the stairs. This is the hardest pendulum trap by far, because the walkway is so narrow and one wrong step will kill you. I ran through each pair of pendulum very carefully; you can not do it one by one, you have to take them in pairs or run through them all at once with 0 equip load.
- Continue on and you will find a few switches on the floor that activate arrows in front of you (after you go up the stairs), and then you will find the next white fog. Traverse it to finally get some fresh air. (make sure you restore your energy to full at this point).
- You can see the giant loading the big boulders into the fortress. You can easily kill him with arrows and he does respawn when you rest at a bonfire. (pre 1.03 he was a good soul farm with 3000 per kill, combined with a nearby merchant)(500 souls per kill post patch).
- A second giant up above will bombard you with firebombs. When emerging from the white fog and facing the stone-loading giant, the firebomb giant will be to your four o'clock and very high up. You can't really touch him at this range, so just be careful to stay close to walls while he throws his bombs. If you kill him (either with arrows or if you reach him in melee) he will not respawn. A good indicator of approximately where he throws the flame boulders is giant patches of scorched earth that you can see as you walk through this area. However, he is very slow (post-patch) and about the only way to get hit by him is to stand in one place for more than 3-4 seconds.
- On the second level (where the second black spot on the ground is), there is a gap in the wall. Drop here to reach a bonfire. The bonfire has a passage that will take you to just before the white fog you just went through, so don't worry about having to do a lot of backtracking. Video
- On the path to the left of the fog gate you can find a couple Balder Knights, and at the bottom, the Flame Stoneplate Ring, which raises fire resistance, useful immediately to mitigate damage from firebombs.
- The Heavy Knight with the mace and shield straight towards the firebomb giant will respawn. He guards the way to the hostile NPC Undead Prince Ricard on the far tower that drops a unique rapier. Undead Prince Ricard is a pushover to your Lightning Spear.
- Taking the bridge up in the sunlight, you will see a T-junction. The left branch leads to an important merchant. You can jump the gap in the bridge fairly easily, but make sure you time it right, and it might be a good idea to use the bonfire you just found just in case. The Crestfallen Merchant sells arrows, armor (including the Onion set), black firebombs, green blossoms, and titanite shards (normal, large and green; 1000, 4000 and 5000 souls respectively). Below his tower, you will find the Cage key which opens a shortcut to the beginning of the fortress, guarded by a snake magician. This key can also be used to free Big Hat Logan (if you did not have the Master Key earlier). Big Hat Logan will be added to your motley crew back at Firelink Shrine.
- You can run and jump onto the platform with the giant. Dropping down from here gets you the Sniper Crossbow and some Sniper Bolts.
- Taking the right branch at the T-junction will take you to a small covered hallway (to your left there is a rapier-wielding balder knight, and a dead end). Take the right turn and you'll see two cages. You can use the cages to be transported to the first bridge you crossed in Sen's Fortress, right next to the snake-warrior. This cage is located on the floor below the fog gate to the Iron Golem boss fight just after the Elite Undead Archer. Warning: you will emerge right in front of a snake guardian. It is also possible to be hit by the pendulum while riding the elevator. Since it can't knock you down it isn't too dangerous, but if you are low in health it can kill you.
- Go around the cages to the left and you'll emerge onto the catwalk the sniper is on. You can run around it avoiding his arrows if you haven't shot him already. He dies very easily. Go through the entrance and you will see the white fog leading to the boss to your left, and a spiral stairway leading to the firebomb giant on your right. The white fog will lead to the Boss of the level, the Iron Golem. Just before entering the fog, however, turn right and go across the bridge to the empty tower in the distance. If you are in human form, you should see a summoning sign to summon Iron Tarkus, whose strong attacks and defenses will prove invaluable in the upcoming fight. After confronting the Iron Golem, stay behind him, but beware of his grabbing attack. You can stagger him and make him fall. He will drop his Core, which allows you to forge his axe. See the Iron Golem page for more information.