Not far to go now.
Dark Souls 3: Cleansing Chapel to Rosaria's Bedchamber
We don't have much more to do in Cathedral of the Deep before we can make a run on the boss, but this last crawl will unlock an important covenant, advance an NPC quest and most importantly open a quick path to the boss.
Note: if you haven't already met him, the route we describe here will prevent the appearance of Unbreakable Patches, whom you need to visit in order to save Siegward of Catarina. However, you can interact with Patches at Firelink Shrine to retrieve the armour instead; see our NPC guide for more information.
From the Cleansing Chapel bonfire, take the lift just outside the second shortcut door. Kill the crossbowman – an old friend of yours – and then go out the opening he was guarding, following the narrow ledge around. Climb the ladder and kill the priest for a Deep Ring.
Always be wary of the lower reaches as you explore this area, because the crossbowmen down there can aggro from impressive distances.
Sniper types can clear the way for themselves here; pure melee should consider this recon for what's to come. Start by looking out the window at the rooftop below and trace it up to where it meets a long flat path. There’s a tall guy with an axe in a little portico. It’s not easy to snipe him, but you can.
Roll out onto the rooftop and lean over the left edge to spot an assassin waiting to ambush. Cross the rooftop, turn right onto the long path and watch the right edge for the telltale fingers of another assassin – staying mindful of the second tall guy in the distance.
Ignore the openings on the left. There are two sloping rooftop paths on the right you'll encounter as you proceed along the long path. The first goes nowhere, but there’s an assassin at the bottom.
There’s an assassin further along the long path you may want to lure in before you reach the second sloping rooftop, where another assassin is waiting to ambush from the ceiling of the little structure. There's an Arbalest at the bottom of the second sloping rooftop.
We’re almost done with this long path. One more assassin is waiting when you run to the end, where there’s a Pale Tongue for your efforts.
Running along this path we have passed two possible entrances to the cathedral rafters. Go back to the one most distant from the Pale Tongue and look across the rafters at the Cathedral Knight. If you put an arrow in him he usually falls to his death, which is highly satisfactory.
There’s a knight with a crossbow out over to the left across the rafters; these bolts hit very hard, so be careful. Over to the right, an assassin is crawling over the rafters – and another Cathedral Knight is patrolling beyond him. With luck, he’ll fall to his death, too, leaving you free access to the Blessed Gem he’s guarding.
Treasure collected and enemies down? Good. Your next goal is a tiny balcony on the opposite side from where you entered, between the crossbow knight and the assassin. Roll down to it, and then one more level.
Rush into the next area avoiding the maggot man mage’s nicely slow magic attacks, and kill him as fast as you can. Turn around and kill all the maggot men who have appeared behind you - or just avoid them, as they're very slow - except sometimes when attacking.
Pull the lever to create a bridge across to the opposite balcony. That’s not where we’re going, though; take the stairs up to kill several more maggot men; they drop from above, so keep an eye on the ceiling, but also be wary of the maggot man mage hidden around the corner from the entrance. The one at the end drops the Red Sign Soapstone, which you can use to invite players to summon you as an invading red phantom. Open the doors and activate the Rosaria's Bedchamber bonfire.
Rosaria herself is ahead. You need to be facing her but a step or two back to speak with her, at which point you can ask to join the Rosaria's Fingers covenant. This PvP clan has the unique benefit of allowing you to change your appearance and redistribute your stats, but you should think carefully before joining; it will close off an NPC quest. See our covenant guide for details, and maybe leave it for endgame.
When you’re ready to proceed, go back and cross that bridge from earlier. Unbreakable Patches, a friendly-ish NPC, appears here if you approach from the other direction by climbing up from around the giant on the ground floor; don't worry, you can go get Siegward's armour from Patches at Firelink Shrine instead. Collect a nearby soul, then follow the totally safe path around to open the main cathedral doors – and thereby, a shortcut back to the bonfire.
Near the doors is a lift shaft you’re apparently supposed to activate from the other direction, so the lever won’t work yet. Drop down (use Spook if you have it, or otherwise have full health and cross your fingers) so you can activate this shortcut.
The chapel ahead is home to two priests on patrol, a Cathedral Knight standing guard in the middle of the room, and another Cathedral Knight sitting on a bench at the front who will aggro as you pass. Two more priests are at the altar.
The boss gates are behind the altar ahead; it's a pretty easy run from the Rosaria's Bedchamber bonfire to here, so you probably want to go and prepare for the battle ahead. Make sure you've saved Siegward of Catarina before proceeding!