In Crimson Desert during Chapter 5, in Main Quest Crowcaller, you will get the objective to track the Invader. The objective will only provide a general search area in Hernand Castle but doesn’t mark the exact spot.
You must go into Hernand Castle and go upstairs. When you enter the hallway in the main castle building, turn right to find a staircase going up.
On the 2nd floor, enter the wooden door on the left. It’s the same door you entered earlier in the story when you were in Hernand Castle the first time.
There you find an Abyss Gate (yellow wall), enter it to be teleported to the Abyss (sky map). If you can’t interact with the Abyss Gate, open the map and press 
and 
on the fast travel point in the sky.
Then go forward to the tower building and defeat the enemies, you get a cutscene afterward and the quest is done.
For more guides check our Crimson Desert Walkthrough.
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