Red Key quick answer
The Red Key is obtained during the main objective Toward the Nushi's Lair. After the first Rangifer fight, follow the Head to Subcity 03 objective, open the concealed surface entrance, descend to the Nushi's Lair Gate: Approach camp, and walk to the sealed gate. Speak to the Retired Gatekeeper Golem beside the gate; the Red Key is awarded in the conversation.
Underground Residential Areas 01 and 02 are not steps on the Red Key route. They are separate branches with similar names. Use the numbered map below and go directly to Area 03 when the objective changes to Head to Subcity 03.
Where Areas 01 and 02 actually are
Area 01 entrance is the eastern of the two early residential entrances. From Cliffside Watchtower, face north and take the right/east surface branch; keep the entrance marker selected until the Underground Residential Area 01 Entrance name appears. This is an earlier story branch, not a passage to the Red Key.
Area 02 entrance is west of Cliffside Watchtower, close to the western edge of the local map. From the camp, take the left/west path and keep descending along the outside route instead of turning east toward Area 01. Stop when the Area 02 entrance marker is directly ahead. Area 02 is optional for this key route.
1Cliffside Watchtower2Area 01 entrance3Area 02 entrance4Area 03 entranceExact route from the Rangifer arena to the Red Key
1. Rest at the Cleanse Walker after the first Rangifer encounter. When the objective reads Toward the Nushi's Lair — Head to Subcity 03, fast-travel to Cliffside Watchtower if it is active. From that camp, face north and follow the objective diamond uphill; do not turn west toward Area 02 or east toward Area 01.
2. Continue to the surface mechanism above the Rangifer arena. Interact with the large rotating crank/lever. The metal hatch opens in the ground beside it. Go through the hatch and follow the only descending ramp; activate Nushi's Lair Gate: Approach at the bottom.
3. Leave the camp through the underground corridor and keep following the main passage until the large sealed gate fills the room. The Retired Gatekeeper Golem is seated beside this gate. Finish the conversation and wait for the Red Key acquisition card before walking away.
1Cliffside Watchtower2Area 03 surface entrance3Gate Approach camp4Red Key / Gatekeeper
Where to use the Red Key
Fast-travel back to the Abandoned Village/nearby village camp. Return to the first talking Rusted Golem in the village, face the ruined buildings, and take the stairs on the left side. The Red Key Door is at the upper end of that short branch; open it and check the strongbox beyond it. This is separate from the final lair gate.
The lair sequence uses the Red, Blue, and Yellow keys. Tailwater Key is an intermediate fourth key used to reach the Yellow Key, so do not mistake the Tailwater door for the Red Key Door. The interactive map keeps all four keys and their matching door markers separate.
Red Key troubleshooting and 100% check
If the key is missing, verify that you are in Underground Residential Area 03 rather than one of the similarly named entrances or interiors. Revisit the Retired Gatekeeper Golem, exhaust the interaction, and scan the nearby ground. If the door remains locked after acquisition, confirm that the inventory notification completed and reload from an activated camp before returning to the marked Red Key Door.
For Kanto completion, verify both entries independently: Red Key and Red Key Door. A collected key does not prove that its optional door branch has been opened. The reward behind that door is not named in the current verified ledger, so this guide does not attach an unsupported item claim to the route.