Complete the "Book of Apocalypse" quests Part 1 to 3.
When u finish Part 3 (The last Knight) you get the Port Lux Mapcode
Where:Talk to the Port Manager At Green Despair, he is located south of the Armorshop keeper. (coordinates x.y: 187.23)
Fort Ruina
* Normal Quests
The Restricted Fort. Ruina (Lv65)* The Missing King
What the Child with the Revelation (Lv65)* The Book of Apocalypse: Part 3
The Last Knight (Lv50)
Where:The warpgate is located South-East of Port Lux Town. (coordinates x.y: 72.152)
Hope this helps! ^^