The Fortress is a ruined castle that Napoleon’s forces have turned into a temporary arsenal, and it sits behind two obstacles that the game never spells out. You can walk up to its gates long before you are meant to clear it, which is exactly why so many players get stuck here. The real barrier is not the enemy at the entrance. It is the poison swamp just beyond him.
Quick answer: You can reach the Fortress gates any time after unlocking the hub, but you only get through the poison swamp after clearing the University and picking up the Shield Transmutation, roughly three-quarters into the game.
Why the Fortress blocks you early
You reach the Fortress through the Abandoned Church, and the path opens as soon as the hub area is available. Early on, though, two things stop you cold.
- A high-level Grenadier guards the entrance. You can fight him before you are ready, but you will not have the health or healing to win cleanly.
- A small poison swamp sits directly behind him. If the poison status builds all the way up while you cross, it kills you instantly.
Even if you somehow drop the Grenadier at a low level, the swamp ends the run anyway. The Fortress is a Metroidvania-style gate, locked behind an ability you earn much later rather than behind raw skill.
The one requirement: the Shield Transmutation
Poison gas is survivable for only a few seconds before William dies, and the Shield Transmutation is what lets you walk through it safely. You pick it up inside the University, so the Fortress stays off-limits until that region is done.
Use Shield Transmutation as a defensive option against foes and hazards in the surroundings. It begins with a 1 damage factor, rising to level 5 at 1.75; perfect parry posture damage is 200. Further upgrades grant projectile deflection, defense against unblockable attacks, and Shield Bash. At the Fortress, you need only the base ability to cancel the poison.
How to open the Fortress for real
Carry a few Nephtoglobin Vials before you go in. They refill your Nephtoglobin so you can keep the Shield Transmutation running through the gas without draining dry mid-crossing.
What’s inside the Fortress
Past the swamp, the Fortress opens into a crumbling castle stuffed with enemies and one of the game’s harder stretches. It is marked as region X and holds 16 chests, with nine notes scattered through its halls. Captain Raphael of the Nephtis Superioris waits as its boss.
| Detail | Value |
|---|---|
| Region numeral | X |
| Boss |  Captain Raphael of the Nephtis Superioris |
| Chests | 16 |
| Notes | 9 |
| Lanterns | Main Gate, Traverse, Chapel, Ramparts, Courtyard, High Tower |
The enemy roster is broad and dangerous, including Abominations, Eternal Guardsmen, Risen Grenadiers, Risen Duellists, Swarm Mothers, and more. Expect this to be one of the sternest tests in the campaign from the moment you step inside.
How to know it worked
You will know you have done this in the right order when Louis directs you to the castle ruins and the “In Ruins” quest becomes active. Crossing the poison without taking damage confirms the Shield Transmutation is doing its job. Once you reach the far side of the swamp and light a lantern inside the castle walls, the Fortress is fully open and you can explore it at your own pace.
