This is a story related achievement and can't be missed. You unlock the prompt to start this mission by reaching level 5
with Loosum Hagar
and completing her previous mission Wasteland Celebrity.Note:
VERY IMPORTANT. If you approach the large bay doors in the side of the mountain and they are open, DO NOT enter this way. You will miss the first mission update marker and end up having to reload the mission.
For any other achievements you might need help with here's my video on all achievements, or check out the solutions for the other achievements, I'll be there