Grave of the Saints

Beware of rats since they can petrify you. Find a Large Soul of a Nameless Soldier in the circular area. You can’t reach the corpse inside the circle so ignore it for now. Head to the next corridor and get Small Smooth and Silky Stones x3 from a corpse to the left.

Backtrack a bit. The corridors here have several Pharros Contraptions. Don't waste any of your Lockstones here except for the one near the ladder you used earlier. Using a lockstone on this specific contraption will allow you to cross a bridge leading to a room with some items. In that room, head to the right to find Poison Moss x2. Continue upstairs to find a Whisper of Despair and Torch. Backtrack again to the bridge and climb up the next ladder.

Once you’ve reached the top of the stairs, an invader will appear along with some giant rats. Take out the rats first before dealing with the invader. Kill him and loot the Homeward Bone x3 from the coffins inside the broken wall on other side of the corridor. Finally, go to the opposite end of the corridor and light up the Grave Entrance bonfire.

Boss: Royal Rat Vanguard

When fighting the boss, keep killing the rats. The indestructible statues may cause your attacks to bounce so be careful. Fortunately, the rats are slow but their numbers can be a problem. After killing a few rats, the vanguard will appear. This doesn't look different from any rats so unless you have AoE attacks, concentrate on that vanguard rat and focus your attacks on him. He's not that tough anyway. After defeating the vanguard, all the other rats will retreat.

Further ahead is the Rat King himself. Talk to him and he will ask you to join his covenant. This covenant is only effective in this territory and within the Doors of Pharros. You'll also unlock the Gnawing Covenant trophy/achievement.

Carefully drop to the hole where the hanging skeleton is to get a Pharros Lockstone from the corpse. You now need to carefully drop using the coffins as platforms. Drop to the central pathway and loot the skeleton in the other end to get a Bleed Stone.

From there, you have to choose; do a sprint-jump to reach the Disc Chime on the broken ledge or drop to the hanging bridge to loot the chest in the other end to get a Ash Knuckle Ring. The former is a necessity for clerics and builds relying on miracles and hexes. Be careful not to fall to the bottom pit as it has exploding undead. The water won't help much with your movement as well. To get the other item, you have to use a Homeward Bone to return to the bonfire outside the Rat King's throne room.

One end of the tunnel exploding undead has a Great Heal miracle while the other end leads to some wooden scaffoldings leading further down. There's a corpse in the lower platform that has a Human Effigy. There's another corpse further in the lower platforms that has a Radiant Lifegem. Continue to the bottom to loot a Token of Spite from the chest. Continue forth and you'll reach The Gutter.