Lost Ark - How to enter the Cube

There are so many little things to learn about Lost Ark. So I thought about doing a quick guide series where there is one question that I will answer in less than 5 minutes. This entry has to do with gaining access to the end game activity Cube. The Cube is located in Vern Castle, but getting in isn't exactly obvious. Thankfully, it's pretty simple once you know how to find the quest.