Quick Answer
The Genma Lab is the Underground Laboratory visited during What Lurks in the Shadows in the Nijo-jo Castle section. Advance that mission to reach it. The mask-door route is near Underground Level Three; Earth-Shakers is in a chest on Underground Level 4, in the room after the fan puzzle. Activate the mirrors on your first visit for an easier return.
- Story mission
- What Lurks in the Shadows
- Area
- Underground Laboratory
- Key item
- Unsettling Mask
- Armament
- Earth-Shakers
Part 1 — Reach the Underground Laboratory
Track What Lurks in the Shadows and follow the investigation into the Nijo-jo Castle area. This is a story location. It is not a separate optional dungeon unlocked by collecting an ending fragment.
When your current objective is elsewhere, progress that objective first. A guide to a lower Laboratory floor will not help you enter a section your save has not reached. Once inside, activate each Spirit Mirror before continuing downstairs.
Part 2 — Open the mask door
Find the locked mask door near the Underground Level Three Spirit Mirror, then keep following the open route until you reach the hanging-mask puzzle. Face the cage and count the masks from left to right.
Use the Oni Bow to shoot masks 3, 4, 1 and 2. Collect the Unsettling Mask from the cage, return to the earlier locked door and use the mask in its mechanism. If a shot breaks the sequence, wait for the reset and enter all four again.
Part 3 — Check Level 4 for Earth-Shakers
Earth-Shakers is the main Armament pickup to check during the descent. After the fan puzzle on Underground Level 4, inspect the next room and open the chest before following the onward objective.
If you are returning only for this weapon, use a Laboratory mirror you activated earlier and work toward that floor. Track the level number as well as the room, since similar corridors can make an upstairs detour look like progress.
Plan a short return trip
Before the final mission, use your save’s available fast-travel destinations to return for missed exploration. Keep a separate manual save before The Clash at Rendaino so you have a clear cleanup point.
For the mask sequence, open the Puzzle Guide. For equipment choices after obtaining Earth-Shakers, open the Tier List or Weapon Build Guide instead of restarting the entire Laboratory route.
Direct answers
Frequently asked questions
Which mission takes me to the Genma Lab?
What Lurks in the Shadows takes you into the Underground Laboratory in the Nijo-jo Castle section.
Where is Earth-Shakers?
In a chest on Underground Level 4, in the room after the fan puzzle.
What opens the mask door?
The Unsettling Mask from the mask puzzle. Shoot the hanging masks in the order 3, 4, 1, 2 to obtain it.