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Cleansing the Land is a main quest and achievement/trophy in the Fallout 4 add-on Far Harbor.

Quick walkthrough

Far Harbor Main Quest: Cleansing the Land
Choose to destroy Far Harbor
Choose to destroy the Nucleus
Speak to Tektus (optional)
Insert Nuclear Launch Key into the Vessel
Go to the wind farm maintenance
Convince Tektus the nuke is the will of Atom
Avoid/Fight the hostile Children of Atom
Enter the kill switch code in the Turbine 003 regulator terminal
Escape the Nucleus within 30 seconds
Return to Tektus
Reward: Far Harbor Survivalist
If The Heretic and Witch Hunt were resolved peacefully, failed, or avoided
If The Heretic or Witch Hunt was resolved aggressively
Return to Far Harbor and speak to Allen
Atom's Bulwark
Crusader of Atom
Atom's Bulwark
Inquisitor of Atom
Reward: 1600 caps

Detailed walkthrough

Cleansing the Land is a quest that requires the Sole Survivor to destroy either Far Harbor by utilizing the wind farm kill switch code, or by using the nuclear launch key and thus destroying the Children of Atom at the Nucleus. Although destroying one of the two factions finishes the quest and grants the achievement Cleansing the Land, the player character can still choose to destroy both factions.

Both codes needed for the destruction are obtained in the previous quest Best Left Forgotten.

When choosing to destroy Far Harbor, one can optionally give the nuclear launch key to High Confessor Tektus. Do note that by doing this the player character can't go back and destroy the Nucleus as well, should they desire so. Tektus will praise them, but then urge them to destroy Far Harbor. To do so the Sole Survivor will have to visit the wind farm maintenance and enter the kill switch code in the Turbine 003 regulator terminal. This shuts down the wind farm, killing off the electricity needed to run the fog condensers around Far Harbor. As a result, Far Harbor will be engulfed in the fog and the creatures that come with it. A message will be displayed at this point that you are now an enemy of Far Harbor. After activating the code and returning to Tektus, the player character will receive Atom's Bulwark. If either The Heretic or Witch Hunt were resolved aggressively, one will receive the title 'Inquisitor' and the perk Inquisitor of Atom as rewards. If they resolved both quests peacefully, failed them, or avoided them altogether, they will instead receive the title 'Crusader' and the perk Crusader of Atom. Both perks have the same effects, and the difference is merely how some NPCs address the Sole Survivor. Then, Far Harbor itself will turn into ruins covered in fog and overrun by creatures, a legendary fog crawler being amongst them. Almost all Harbormen are dead, with only a few making a desperate last stand.

When choosing to destroy the Nucleus the player character will have to insert the nuclear launch key in the Vessel. Doing so will turn all Children of Atom hostile and will initiate a 30 second countdown upon which the submarine will go into lockdown, followed immediately by the launch of the nuclear warheads. As long as the key wasn't given to him, is also possible to convince Tektus through speech checks that it is the will of Atom to launch the nuke, which will allow the player character to leave the Nucleus without being attacked. The Sole Survivor has 30 seconds to leave the Nucleus. Once outside the building, one will be safe from the explosion. Once the Nucleus explodes, the player character will be given the perk Far Harbor Survivalist. Upon returning to Far Harbor there will be a commotion, with Harbormen gathering around and Captain Avery announcing that there was indeed a nuclear detonation and that all Children of Atom are dead. Allen Lee will react happily about the news, but Avery will insist upon a moment of silence.

When talking to Allen he will call the player character a hero and reward them with 1600 caps.

Quest stages

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Quest stages
StageStatusDescriptionLog Entry
10 Locate the Nuclear Launch KeySeems DiMA uncovered the location of the launch key for the submarine in the Nucleus. I'll have to get into the safe room in the Harbor Grand Hotel. Luckily, I've got the code - 485130.
20 Bring Down Far Harbor's Defenses
Confront DiMA about the Wind Turbine Kill Switch
I recovered the code to activate the kill-switch installed in Far Harbor's wind turbine. I suppose I could either confront DiMA about this... or I could just pay the maintenance shed a visit.
I recovered the code to activate the kill-switch installed in Far Harbor's wind turbine. If I want to use it, I'm going to have to pay a visit to the farm's maintenance shed.
120 Listen to Safe Room Security TapeAppears the Harbor Grand Hotel safe room had an old recording system. Maybe it can point me to the launch key.
130 Obtain the Nuclear Launch KeyThe launch key is hidden on a boat at Fringe Cove docks. Safe combination is 44, 6, 75, 12.
150 Use the Launch Key to Destroy the NucleusI've found the launch key that could destroy the Nucleus. If I use it, it could change the future of the whole island.
Confront DiMA about the Nuclear Launch Key
210 Escape the NucleusI triggered the countdown to launch the nuke! I need to get out of the sub bay! Why am I reading this?!
250Quest finishedIt's done. The fate of the island has been decided. The Nucleus is no more.


  • Finishing this quest will fail the quest Safe Passage.
  • Before destroying the Nucleus, one may wish to purchase the Recon Marine right arm and left arm, two legendary pieces of Marine armor, from the vendors there.
  • The holotapes, notes, logs, etc. encountered while obtaining the launch key tell a story with implications of the cause and beginnings of the Great War.
  • If you finish the quest Reformation, you will fail the optional "Talk to the High Confessor about the Nuclear launch key", as it is directly tied to the final stage with destroying the Nucleus.
  • In turn finishing this mission will fail Reformation completely.
  • If the player character previously convinced Uncle Ken to return to Far Harbor during the quest the Hold Out, and then destroys Far Harbor and enters the Last Plank, Uncle Ken may be found fighting an angler. Despite all Harbormen being aggressive towards the player character, Uncle Ken will not act hostile but will not comment or acknowledge the destruction of Far Harbor either.


  • Icon pc.png Icon ps4.png Choosing to use the launch key and then staying in the Nucleus to watch the launch may crash the game.[verified]
  • Icon pc.png Icon ps4.png Icon xboxone.png Confronting DiMA about the wind turbines or the nuclear launch codes might not be possible, despite him being an active quest marker. Maybe it is caused by Reformation already in progress. It may also be impossible even without the Reformation quest started.[verified]
  • Icon pc.png Icon xboxone.png Taking actions that make the Children of Atom hostile, such as killing Grand Zealot Richter, before obtaining DiMA's memories and starting Cleansing the Land will prevent the dialogue option to confront DiMA about the nuclear launch key from appearing.[verified]