Archdragon Peak is the Secret Area in Dark Souls 3 and once you get there you will have the chance to grab the Dragon Armor set which will transform you completely into a Dragon. To get to this secret area you must know the Dragon Gesture and the location to get there is shown in the guide below.
How to get to Archdragon Peak Secret Area
Archdragon Peak is a Secret area which is owned by one of the Dragon. You will need to learn the path of the Dragon Gesture which can be found inside the wrecked area after defeating Oceiros(woods below Lothric castle). Once you get inside the Room head down and you will be fighting an enemy here. Kill him and head to Corpse with the White orb there.
Note: From The Lothric Castle you can Enter Untended Graves Secret Area
Once you pick up the Dragon Gesture, now head to the prison area by The Boreal valley. Now that you have learned this new Dragon Gesture, you must use it to get to the Secret Area. So from the prison area get outside near where the shortcut elevator and from there’s a few knights and dragon looking people looking out to a palace on a cliffside. Use the Path to the Old Dragon Gesture on the unoccupied rug. Wait for 5 seconds and a cutscene will play and you’ll get transported there.
How to get the Dragon Armor Set
Now Explore the secret area and make sure you pick up each and every item before getting inside the Castle. Once you get into the Boss fight will start where you need to fight against the “Ancient Wyvern” as well as “The nameless King“. It is very easy to take him down to do it fast and take away the Dragon Headstone which is used to turn your head into a dragon.
With this new Head you can breathe fire and to completely transform into a dragon you must get the Dragon Torso Stone. Remember once you undress and turn into a dragon you cannot get back to the regular form unless you die. Also, you cannot equip while you turn into a dragon. So thus completing the guide and make sure you visit our Dark Souls 3 Wiki Page, to know more about the game, collectibles and Boss Fights.