Lost Avos City

The Lost Avos City is a Secret Discovery located in the north of Corkus Province, near the Avos Territory. It involves locating and exploring an ancient, buried city of the Avos built 350 years ago, and expands on the lore and history of the Avos following the arrival of the humans. In addition, at the end of the city is a secret boss battle and extra reward. A minimum level of 85 is required to gain the Discovery's experience reward.

Finding the City
Unlike most Avos settlements and homes, there is one abandoned Avos hut outside of the Avos Territory, on the ground level mostly dominated by the Corkian Humans. This site is mentioned as unusual by a Corkus Citizen in Corkus City.

To begin the process of finding the Lost City, just enter this hut (be wary of the many hostile rogue Mechs that spawn nearby, as you could get trapped inside by them). A ghostly Avos simply called ??? will appear behind you, in the doorway; right-clicking it will cause it to vanish and reappear some distance away, to the north. Keep following this ghost north, right-clicking it each time to make it appear at its next location, until you reach a cave in the cliffs.

This cave is also full of dangerous mobs, so be prepared to fight them off. After interacting with the Avos ghost at the cave entrance, follow it twice more into a large room with a ledge, where it will now be found. This chamber also holds two Tier III Loot Chests. Right-click the ghost one more time to make it disappear and open a secret passage in the wall, which will teleport you to the subterranean Lost Avos City. Simply walk forward to achieve the Discovery, and gain 1060000 experience points.

Exploring the City
Although you will now have reached the Lost City, there is still much more to explore within it. The city is a somewhat labyrinthine, dungeon-like ruin, and you will often have to take in your surroundings carefully in order to find the way forward; it is rarely obvious, and there are many dead ends. In addition, the ruin is haunted by level 93 Fallen Avos Warriors and level 91 Fallen Avos Shamans, who use melee and ranged attacks respectively, and who can be very dangerous in the tight corridors and chambers of the city. The Shamans especially can be annoying during the brief parkour areas.

Despite its vastness, there is a correct path through the Lost City that will take you deeper into the ruins. In addition, you will get bits of dialogue from a mysterious voice as you progress; this dialogue slowly reveals the history of the Avos and the city itself, as well as the arrival of the Corkian settlers (see below). Over time, the voice will reveal itself as the immortal Phoenix Prince of the Avos.

At the far edge of the city is a great ruined palace, overgrown and empty, that belongs to the Phoenix Prince. On its roof is a dark passage that leads to the grand throne room where the boss battle with the many forms of the level 120 Phoenix Prince takes place; the final lines of dialogue appear as you enter the chamber. Defeating the Prince is the final challenge of the Lost City, and he drops a powerful level 90 Legendary helmet, the Phoenix Prince's Crown.

Dialogue
[1/12] ???: It was 350 years ago when I last saw a human. And I will never forget. [2/12] ???: Your kind had already dominated Wynn and Fruma. But you decided to come to this island. Our island. [3/12] ???: I will never understand why some Avos decided to let you live here. Those who welcomed you stayed on the surface. [4/12] ???: But I, Prince of the Avos, led the rest of my people down here, where no human could disturb us. And so, we lived here... for a while. [5/12] ???: But avians like us are not suited to living underground. We became ill and lost our feathers. And eventually, my people died out. [6/12] ???: Their souls still wander and cry throughout the ruins of my city. [7/12] ???: However, I have remained here, still alive, hearing the plight and torment of the lost souls. For I am cursed to never die, only to be reborn. [8/12] Phoenix Prince: Because of this endless cycle of reincarnation, I am only known as the Phoenix Prince. [9/12] Phoenix Prince: After the death of all my people, your kind sealed the city, they likely didn't want anyone to know about what happened down here. [10/12] Phoenix Prince: But unbeknownst to them, I was still here. Trapped forever, without even the escape of death. And it is all the fault of the humans who drove us here. [11/12] Phoenix Prince: You're an invader, just like the rest of your people. They do not deserve to live on this island... on our island. [12/12] Phoenix Prince: Prepare for our revenge. Prepare to DIE!

Tips

 * It can be difficult to locate the Avos ghost after leaving the abandoned hut, but follow the nearby road north and you'll see it.
 * If the ghost despawns or doesn't reappear while you're following it, you'll have to restart the process by switching to a different server.
 * Inside the Lost City, paths of grey, brown or red carpets will sometimes show the correct path.

Trivia

 * The Phoenix Prince is a reference to Phoenix King/Fire Lord Ozai from Avatar: The Last Airbender.
 * His primary elements are fire and air.
 * The last two lines of dialogue he says is similar to what Ozai says when he corners Aang in the episode Sozin's Comet Part 3.