Registered to repost the guide link shown by @Wight above. The original link was gone for good due to management shift from KAKAO to PEARL ABYSS.

Taken from Wayback Machine. The original post was taken from:
http://forum.blackdesertonline.com/index.php?/topic/134373-grave-of-a-king-quest/

-------- CREDIT TO KELSTULTOOR --------

Posted 6 Mar 2017 (edited)

Hi guys, I didn't found anything about this quest online and I've seen a lot of people seeking for the answer!

So I wanted to share with you the right info to make it through this quest.

I didn't pay attenction at the beginning and I just went to the Valencia Castle trying to dig around. that's what you are suppose to do in 5 easy steps.

Click on the device in your inventory:


It will bring you in the underground tomb.


Once there, click again on your device :


It will cast a mini boss (Defense Ordnance)


Kill it and you will be done


OkThanksBye

Edited 24 Nov 2017 by KELSTULTOOR

Helpful Guide shown with pictures:
http://forum.blackdesertonline.com/index.php?/topic/134373-grave-of-a-king-quest/