For those of you guys who want to explore the entirety of the DS3 world, but are having trouble figuring out how to get to Archdragon Peak.
To get to Archdragon Peak, first up you have to go to the Consumed King’s Garden. What you do is, once you defeat Dancer of the Boreal Valley, you go up the ladder that drops down after the fight and go left, instead of straight ahead[going straight will lead you towards the main quest-line]. You fight a big-sized enemy here and then take an elevator which leads you straight down to the Consumed King’s Garden.
At the end of the area, you fight Oceiros, the Consumed King. After defeating him, open the double doors at the other end of the arena.
You now pass through a small corridor, at the end of which you fight a manserpent. The corridor opens into a huge hall with a few treasure chests to open. You’ll also see a statue/fallen soldier in a sitting position, and in his lap is an item to collect. This “item” happens to be the Path of the Dragon emote[courtesy Gamespot for the image].
[NOTE : Go down the hall, open the treasure chest at the far end, then hit the wall to open up a new path. This route will take you down to the Untended Graves, where a dark secret awaits your journey’s end.]
Now, from here, you need to go to the Irithyll Dungeon bonfire. Go through the prison area, passing the jailer guys on the top floor, and go down the stairs on the other side[where 3 of them jailer guys are waiting for you, along with a skeleton-filled cage]. After speedrunning/killing the enemies, go to your right and open the door. Go on and take the elevator; it’ll take you down. You’ll come to this place.
Now. go near the dragon-like thing, and use the Path of the Dragon emote. Sit for about 5 seconds or so; a brief cut-scene will play, followed by you getting transported to Archdragon Peak. Hurray!