Captain’s Key is on the ground in the lower passages of Fortress, near the Chapel route. Take it back to the locked building by the Traverse Lantern to reach a chest containing a Ferrofluid Flask Power Upgrade. It opens a different room from the Fortress Armoury Key.
The important distinction is between where you collect the key and where you spend it: search the Chapel passages for the pickup, then return toward Traverse for its door. Do not keep searching the room where the key was lying for the upgrade chest.
Find the pickup near Chapel
The collectible route places Captain’s Key in the underground section associated with the Chapel Lantern. Use the room containing the trapped Quintessential Blade Material chest as a nearby landmark.
- Return to the passage opposite that chest room and descend the stairs.
- At the bottom, continue to the room at the end of the passage. The nearby room on the left contains a sword planted in the ground; that is a separate bonfire interaction.
- Search the right-hand corner of the end room for Captain’s Key lying on the ground.
Collecting the key is the purpose of this detour. You do not need to treat the planted sword as the key or light it to obtain this pickup.
Open the building by Traverse
Return to the Traverse Lantern. Face away from the area with the cannons and look for the locked building. Use Captain’s Key at its door, enter, and open the chest containing the Ferrofluid Flask Power Upgrade.
This is a healing-power upgrade, rather than a new weapon or another key. The key’s pickup location and the chest’s location are separated by the Fortress route, which is why returning to Traverse matters.
Keep the two Fortress keys separate
| Item | Where the collectible route places it | What to do with it |
|---|---|---|
| Captain’s Key | Ground in the end room reached by the lower Chapel stairs | Open the building by Traverse, opposite the cannon area. |
| Fortress Armoury Key | A platform at the top of a ladder in a different interior room | Open the Fortress armoury door; it does not replace Captain’s Key. |
If you already have the Fortress Armoury Key but cannot open the building at Traverse, check the exact item name in your inventory. The two doors are separate pickups in the same region, rather than alternate names for one lock.
Related routes
- Follow the Fortress progression route.
- Find the Mining Shaft Key in the Caverns.
- Understand Ferrofluid Flask upgrades.
Source and route limits
PowerPyx’s Chapter 9 collectible route supplies the Chapel landmarks, the key pickup and the door by Traverse. Another collected Fortress guide starts the detour from Ramparts, but the supplied material does not establish an exact connection between those approaches. This page follows the Chapel landmarks rather than combining the two into an unverified turn-by-turn route.