The Cartenon Temple, also known as the Double Dungeon, was a mysterious hidden dungeon that appeared within two separate D-Rank dungeons in the story. It also served as the base of operations for the Architect, the moderator of the System.
In what seemed like just another ordinary D-Rank dungeon raid, Jinwoo and the rest of his raid party discovered a second hidden dungeon inside the gate and decided to scope it out. Unfortunately, they realized too late that the dungeon was a trap and found themselves locked in with no way out.
Although they were eventually able to satisfy the conditions to get the doors open (primarily thanks to Jinwoo), by that point only six of the seventeen hunters were still alive, the rest of having been killed by the statues inside the dungeon. Realizing that one person had to stay behind for the rest of the party to escape safely, Jinwoo volunteered to be the sacrifice, as he had already lost his right leg.
As the statues skewered him with their weapons and threw him around like a rag doll, a strange message suddenly popped up in front of Jinwoo's face, telling him that he completed the requirements for a hidden quest and asked whether he wanted to accept or reject his status as a Player. With no time or options left, Jinwoo accepted, making him the Player of the System and allowing him to survive the Double Dungeon.
When Jinwoo reached level 100, the Architect invited him back to the Double Dungeon so that the Shadow Monarch Ashborn could take control of him as his vessel and finally descend into the human world as they had originally planned. After Jinwoo passed his test with flying colors by defeating both him and his statues in a series of brutal fights, the Architect put him in a trance and waited for Ashborn's arrival.
Unfortunately for the Architect, however, Ashborn had no intention of taking control of Jinwoo as his vessel and wished to transfer his powers instead to make Jinwoo his heir. As a result, he chose to betray the Architect by locking him out of the System and giving Jinwoo the black heart. Although the Architect eventually realized Ashborn's treachery when Jinwoo regained control of his own body, he was unable to do anything to defend himself, as Ashborn had stripped him of his power over the System, and was left wide open when Jinwoo sliced him to pieces, killing him on the spot.