Locked Door In Road of Sacrifices

[Killer Kitten]

There's a locked door by the Black Knight in the Road of Sacrifices. I am getting sick and tired of guides pointing it out, but not saying how to get through it! If it's in a different area, why don't they just say so, so don't have to thumb through their entire guide on how to do it?

FYI, I'm trying to back track through all the areas of the game before heading to the final boss. I do this in every soulsborne game. So please, none of this stupid, "Oh, don't worry about it. The way through it further down."

Just. tell. me.

[Silent Warrior]

You can open this door from the other side, from outside the Abyss Watchers boss room. From Abyss Watchers go out into the forest and hug the left wall, until you reach a path through a hallway. Follow this path, there will be a bonfire "Farron Keep Perimeter" . Now only a few steps further and you'll reach this door.

In case you're talking about the other door behind the Black Knight, this one is not possible to open, it's blocked by some rubble.

[Myr]

If you do want to farm Black Knights at some point using that shortcut and its bonfire is very safe and effective as the enemies on the way start passive due to looking away from the bonfire direction and if pulling with a bow from the door the crucifix guy outside wont see you, it also cuts out the pvp chance from the crab swamp