Abyssal Dungeons are an endgame dungeon event that must be completed with other players in order to earn rewards and level enhancements. But, how do you actually unlock these dungeons?
Like most things at the endgame, you will have to first be Level 50 before being able to unlock Abyssal Dungeons. This is mainly because the enemies found in the dungeons couldn't possibly be fought against otherwise.
You'll then need to have completed the main World storyline so that you can unlock Chaos Dungeons and Guardian Raids at Vern Castle in the North Vern continent. Then you must complete the Ancient Elveria dungeon at the Abyssal Dungeon location on the map.
It is important to note that in order to start the dungeon, you must have an Item Level of 340.
Once you have successfully completed the dungeon, you will speak with an NPC that will subsequently unlock the Abyssal Dungeon. At that point, you can begin participating in Abyssal Dungeons at the Abyssal Dungeon Board in the Military District where the other dungeons and raids can be found.
For more Lost Ark, check out Perception Shards: What are they and How to get them in Lost Ark on Pro Game Guides.