How to unlock: The quest is unlocked after you finish The Cold, Calculating Jack main quest.
From the conversation with Matkina, during the quest The Cold, Calculating Jack, you can learn that you need to get to Valley of Dead Heroes. However, you can't get there "on foot" which means that you must use some form of transport. Airships are located in Caravanserai so when you get there, head to Master Rennio (M7.2).
Ask Master Rennio about the flight to Valley. This situation can play out in two ways. The first way is to pay 600 shins. The second is to complete The Airship Thief side quest, which is related to a potential team member Erritis (this quest automatically begins when Erritis is a party member during the meeting with Master Rennio).
Regardless of what option you used, Master Rennio gives you some time to prepare for the journey. Use this time to complete all of the optional quests in Sagus Cliffs because when you leave the city, all active side quests are cancelled. It is also recommended to rest because when you get to Valley of Dead Heroes there is a possibility that you will have to fight. But you don't have to "clear" your inventory because in the Valley there is a new merchant.
Warning - If you incited the crowd during State of Execution side quest then Ris swore that he will get his revenge on Tybir. He can appear here and try to stop you from leaving the city. Use intimidation or defeat him in fight (more details in the guide for this quest).
After you get to the Valley of Dead Heroes you must fight with a suspicious group.
When you arrive in the Valley of Dead Heroes you will immediately meet a group led by Klin'Kar, representing the organization called Children of the Endless Gate. Klin'Kar demands from the hero that he must find two Memorialists that are hiding somwhere. You can answer him in several ways:
- Attack Klin'Kar and his thugs - This is a rather difficult fight because the enemies have advanced skills. After the fight, Beltrax, one of the Memorialists, will arrive. He asks you to deal with Children of the Endless Gate that took over the Valley. From the Memorialists you will get the Endless Horror side quest (the guide for this quest can be found in the chapter dedicated to the Valley of Dead Heroes).
- Agree to find them - The Memorialists can be found in the cave, behind the boards (you can go past Klin'Kar and his henchmen until you finish the quest). You can help the Memorialists by covering their tracks or kill them by taking the stone which causes the cave to collapse. You can also order them to go out and let the Children of the Endless Gate do the execution. If you directly or indirectly caused their death, you will receive The Caretaker's Riddle side quest from Children of the Endless Gate (the guide for this quest can be found in the chapter dedicated to the Valley of Dead Heroes).
- Intimidate/use persuasion on Klin'Kar and his henchmen - This solution allows you to persuade Children of the Endless Gate to leave you without a confrontation. After that, the Memorialists leave their hideout and ask for your help. If you agree, they will give you the Endless Horror side quest (the guide for this quest can be found in the chapter dedicated to the Valley of Dead Heroes).
No matter how you acted after arriving in the Valley, you must reach the Necropolis. There you will find the portal to the First Castoff's Tomb. Move towards the central part of the map and use the portal Light Minnim (M12.3). It will take the party to the eastern upper walls. You can reach their northern part, where the entrance to the Necropolis is located.
After entering the Necropolis you will encounter Motley, a member of the Children of the Endless Gate. He will hod new Materialists and he will be trying to obtain the password to the lock from them. The lock blocks access to the terminal in Necropolis (M13.3). It is a serious problem since without neutralizing the lock you won't be able to use the teleport to get to the Castoff's tomb.
You can act in two ways:
1) Help the Children of the Endless Gate in obtaining the password. If you want to help the cult members, you can offer your services during the conversation with Motley. It will be easier if earlier you helped Klin'Kar - he will recommend you. Otherwise you will have to use Persuasion. You won't obtain the password through the conversation with the captured Memorialist Talira Kyo. Instead, you must return to the Valley of Dead Heroes and go to the Memorialist camp in the western part (M12.6). Speak to Ronos Cai'Sul and use deception to obtain the password (Guni).
Tell Motley the password and the lock will be removed (M13.3). You will receive 25EXP. You can let the cult members murder the Memorialists or defend them. In order to scare the cultists from the necropolis, you would have to use Intimidation and Deception (Motley would leave a note with the code behind).
2) Save the Memorialists by attacking the Children of the Endless Gate. If you want to help the Memorialists, you can decide to attack the members of the Children of the Endless Gate. You can do it after entering Necropolis or after the conversation with the imprisoned Talira Kyo. Winning the battle with the cult members isn't very easy, although despite the advantage in numbers they can quickly die. First you should eliminate the "elite" enemies and then focus on the regular ones.
Once the battle is over, speak to Talira Kyo about deactivating the whisperlock (M13.3).
Both options described above have the same main objective - removing the whisperlock which made it impossible to use the terminal in Necropolis (M13.3). Once you do it, interact with the terminal and enter the code 3431 the party is aware off. This will take you to the First Castoff's Tomb (M13.7). Begin by investigating two interactive friezes on the right side of the tomb. Then, approach the huge door and choose the first action from the menu (touching the door with your head in a same manner as seen during the mere) to unlock them. This will unlock a portal to Miel Avest. You will receive 100 EXP and a new main quest will start - The Sanctuary of Miel Avest.
Important - Before you leave Necropolis and Valley of Dead Heroes, try completing other side quests in this areas and visiting the remaining tombs (their list can be found on the page with the description of M13 map). In addition to that, you should rest before using the portal.