Not Alone is the first story mission of the Alpine Unrest DLC. You will get it in your Main Mission log to go to a marker in the Forest Region, east of Ostervik. The initial description is as follows:
"At last, you've found proof that there are other survivors out there. North of the IGA Facility in the Forest Region, there's a convoy that was dispatched by the Swedish Army in the direct aftermath of Cataclysm Day; in one of the trucks a computer terminal connected to a radio picked up a looping message of Anita Sjorgren calling for survivors.
She seems to be with a small group somewhere on Himfjall, a ski resort located east of Ostervik, and her group is trying to set up a makeshift boat passage to and from the island."
Reaching the convoy, you will be tasked with repairing a radio, which will lead you to the dock at Lennarts Marin AB, to the NNE. Once there you will need to destroy a handful of Runners, find a walkie-talkie then a wheel to fix the pulley to get the boat ferry across the river. You will encounter a single Runner on the dock on the other side, then unlock a makeshift Safehouse.
You will then be tasked to earn the trust of the survivors by going to the village of Marksatern, to the east (there will be a church along the way, but this one is not a Safehouse). Once there you will be tasked with destroying three Apocalypse Class Runners, then find Roland in the cafe. He will be dead, unfortunately, but this will complete the quest and unlock the achievement.