Already past this part? Head over to the Cave of the Dead with part 2 of the Dark Souls 2: Crown of the Sunken King guide.
First thing's first: to access the Sunken King content, you need the Dragon Talon item. Make sure you obtained it from purchasing the DLC. With it in hand, you can go to the Black Gulch and find the room where you fought the Rotten. The rightward wall has a room that leads to the Primal Bonfire. Find an obelisk in the back, and it will take you to the DLC area. Before you go in, make sure you have plenty of ranged attacks for this area. They're helpful for both combat and puzzle challenges.
Shulva, Sanctum City
Once you enter the area, head down the path and ignore the huge dragon above you. You'll come to a bonfire, and right beyond that is your first enemy encounter. It's just a single one, so dispatch it quickly and continue going up the hill. Here you'll see a glowing pillar on the left, so hit it to raise a structure and hurt the enemies nearby. Head forward--you can't make it to the areas on the left anyway--and then take out the three enemies before moving on again.
When you crest the top of the hill, four more enemies will be waiting for you. They're all ranged, so respond with your own range or close the gap to melee them quickly. Grab the Lifegems from the second hill, and then hit the glowing pillar to raise another structure. You'll have to move quickly to get to the structure as it rises, but being at the top will let you jump ahead to find a Dark Quartz Ring +3.
You can now reach another set of enemies in the lower area, so take them out and pick up a Poison Stone item. You'll see stairs on the far side, so head up them into a room full of red objects. Attack them with your ranged equipment to nullify their dangerous effects, and then go into the room to pick up some Goldenfruit Balms. You'll also find a couple of insect enemies, so take them out and then use the door on the right. Some enemies might notice you, but whether they do or not you should used ranged equipment to defeat them.
Head through the doorway on the other side to find a few Old Growth Bombs. You can use the ledge to the right of the doorway to reach them, but you'll need to time your jumps very carefully. Collect them or not; either way you'll go through the staircase back to the entrance area. You'll find a pillar next to the white crystal formation, which you can use to get back to the first bonfire. Use a ranged attack to deal with the insect on the far wall, and then head inside the structure to find another enemy. Defeat it and go upstairs to find a Poisonbite Ring +1.
Now you have a choice. You can go left to beat the last enemy, or just continue forward, or drop down to find five Lightning Urns. When you're ready to move forward, to back towards the room with the red objects and get to the structure above the pots. Hit the glowing pillars to raise a walkway, then hit another glowing picture to raise the next structure.
You can now drop down to the ledge below. Some insects are on the second floor, so if you have a ranged attack you can beat them easily from here. Once they're beaten, go upstairs to find the Elizabethan Mushroom. You can drop through the other opening here to go down to level 1A.
Go down the stairs to find the walking poison statue near a wall. Attack its feet to do damage; this kind of attack is easiest with a ranged weapon, again. You'll find 20 Throwing Knives and 5 Cracked Red Eye Orbs near where it was originally standing, and then find one more enemy to the left. Once they're finished, head down the stairs.
Just beyond the stairs, there's a ramp to the left that leads to the Dragon's Sanctum and Cave of the Dead. For now, proceed forward to find a small set of stairs that lead to a building on the left. Take down the enemy and go through the doorway, then head down the path to the right to find a Sanctum Mace. Go back down the stairs to find fur more enemies, after which you'll find three Twinkling Titanite on the ground. Take out another poison stone enemy, then climb up the ladder nearby. Cross the rooftops to find another bonfire, and then find a Dried Root through the doorway. Drop down to return to the beginning of the area.
Go down the stairs and then to the right, and continue down the ramp. You'll find two more enemies here, so beat them and then go across the bridge and down another set of stairs.
Take the stairs to the left to cross the bridge. You'll see two enemies there who will be killed by a dragon. If you have a ranged attack, though, you can beat them before you reach that area. Break some pots and then head across.
Go down the stairs and hit the switch on the left to find a Soul of a Great Hero and three Dragon Charms. Get them adn then head through the hallway on the other side. Use your ranged weapon to do as much damage as you can to the enemy just ahead, then go down the stairs to the left to finish him off. Two more enemies are in this room as well, but first focus on attacking the bodies on the altars. Open the five chests in this room to get a Titanite Slab, five Old Growth Balms, one Soul Vessel, one Catarina Helm, and 50 Destructive Greatarrows.
A few more enemies will fight you in the next hallway. They have long reach, so make sure you give yourself some space to fight them by entering the previous area. Defeat them, and then head into the hallway again. Be careful for the pressure plate in the middle of the hallway. Two more enemies in here will be "sleeping," so hit them for as much damage as you can before going further.
Be careful not to head too far down this next hallway, or a sorceress will attack you. Fight the two enemies near the entrance first so you won't have to deal with them and the corceress all at once. Once you've dealt with them, open the coffer and have your shield at the ready to prevent damage from a series of arrows. You'll find a Bonfire Ascetic inside.
You can pick up a Human Effigy from the far wall, then use your ranged attacks to kill an enemy visible through the hole in the door. You can then step on a pressure stone to rotate the door. Do this repeatedly until the large opening is at the bottom, and then head through. Go down the hallway and stairs, and then head left at the junction to find a Repair Powder. Continue straight, jump over the gap, and head down until you find a closed doorway. Use ranged to hit the switch and then go through the opening. Then, head down the hall and use a ranged attack on the switch.
Go through the doorway that just opened and deal with the melee enemy before dealing with some others on the far side. Approach the top of the stairs cautiously, since there's a pressure switch that triggers a spike trap. Go down another set of stairs to find a Soul of a Hero and Human Effigy, along with three chests that have three Boltstones, three Bleed Stones, three Twinkling Titanite, three Petrified Dragon Bones, and a Puzzling Stone Sword. You have t have hit the switch on the previous hallway to access the Puzzling Stone Sword.
Go back to the hole you jumped over before, and this time fall through it. Move away from the sharp corner, and instead go down the stairs while being careful of the spikes. Use ranged attacks from the stairs to take down the enemy, or just get his attention so he walks into the spikes himself. Navigate carefully through the spikes to get several items. Near the first enemy are three torches, and the far right has Twinkling Titanite, five Holy Water Urns, a Human Effigy, and a Dragon Stone in a chest that can be accessed by hitting a switch on one of the pillars. You can take a narrow path between two sets of spikes to go towards a boss battle, but first you should go up the ladder on the right side. Climb up, defeat the sorceress, then head forward to fight another sorceress. Then you can turn around and head to the end of the path to get to a bonfire, and go past it to find the Sanctum Crossbow.
Go back where you came from and take down the sorceress. Another enemy is in spirit form. Go to the right of the entrance to another bridge, and then down the broken stairs to find a Bloodbite Ring +1. Go back up the stairs and fto the left to find a room with three more spirit enemies. Attack the statues to make them materialize, and then defeat them. Head down to find an Eternal Sanctum Key and a Sanctum Knight Helm. Then go back into the area with spikes and up the stairs to the sharp corner, and into the next area.
Your journey isn't over yet! Head over to part 2 to find out how to defeat The Cave of the Dead.