Cleansing the Land Cleansing the Land is a main quest and achievement / trophy in the " Fallout 4 " add - on " Far Harbor " . 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 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 the player can optionally give the nuclear launch key to High Confessor Tektus . Do note that by doing this the player can ' t go back and destroy the Nucleus as well , should they desire so . Tektus will praise the player , but then urge them to destroy Far Harbor . To do so the player 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 will receive Atom ' s Bulwark . If either The Heretic or Witch Hunt were resolved aggressively , the player 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 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 to leave the Nucleus without being attacked . The player has 30 seconds to leave the Nucleus . Once outside the building the player will be safe from the explosion . Once the Nucleus explodes , the player 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 a hero and reward them with 1600 caps .