This may be a small location but it’s infested with rats. Use the Pharro’s Lockstone, defeat the Rodents of Unusual Size and the Royal Rat Vanguard.
Go through the entrance and kill the two zombies as you step through, then the four rats. The rats are fairly easy but they come at you from all angles so don’t underestimate them. Near the open doorway you’ll find a Large Soul of a Nameless Soldier which you can pick up as you go through and up the stairs.
Another four rodents will come at you from the right. Once they’re done with make a mental note of the face on the floor near the top of the stairs. Go left, kill the zombie and take the Small Smooth & Silky Stones. Now go back to the face and use a Pharros' Lockstone. You can ignore all other faces from here on in as they don’t do anything and you’ll only be wasting items.
Now go across the bridge and into the next room where you’ll be attacked by rats. Once they’re dead, take the two Poison Moss. Head upstairs for a Whisper of Despair and a Torch. Go back to the bridge and on the left is a hall with a ladder that will take you to the next floor up.
You’ll have to fight Rhoy the Explorer here and two rats, so take the rodents down quickly then focus on Rhoy. On the other side of the broken wall are three Homeward Bones. Go down the other end of the hall for a bonfire, but kill the two rats first.
Down the corridor is the next section (through the mist) where you will fight loads of rats and the Royal Rat Vanguard. Don’t forget to light the bonfire.
Boss Battle: Royal Rat Vanguard
Reward: Royal Rat Vanguard Soul, Rat Tail
The amount of rats during this fight can be overwhelming and if you take too many hits you will become petrified. Equip anything resistant to petrification if you have it (the Ash Knuckle Ring found in The Gutter, for example). And the Royal Rat Vanguard poisons when it attacks, so anything that prevents poisoning will be useful too.
Despite the threat of being petrified and poisoned this is an easier boss fight than most. Kill rats as soon as you enter the area and keep moving so you don’t get overwhelmed. After a minute or so the bosses’ health bar will appear.
Now you’ve got to try and pick out one rat amongst many. It’s the one with a black furry back. Lock onto it and keep locked on to it.
The Royal Rat Vanguard isn’t very tough so just hack at it until it’s dead - honestly, it won’t take much effort. Once the Vanguard is dead the rest of the rats scurry off. Kill them for extra souls if you like.
Go through the doorway that was blocked by mist and speak with the rat on the pile of bones. If you want to obtain the rat’s covenant he’ll gift you the Crest of the Rat.
Now go down the corridor on the left and drop through to arrive in the same spot you started. There’s a Pharros' Lockstone here. Drop down into the next area and walk past the coffins to the left, down the coffin stairs.
You’ll arrive at a stone bridge but not before taking a little damage from the drop. There’s a Bleed Stone at the far end. Now go back the opposite way along the bridge. On the right and below is a Disc Chime on a small platform.
Now before you drop lower be prepared to fight a couple more enemies as this is the room at the bottom of the well in Majula that leads to The Gutter.