Spec Ops: The Line
50 Achievements
15-20h
GOG
Treacherous Ground
Look out below.
71.1%
How to unlock the Treacherous Ground achievement in Spec Ops: The Line - Definitive Guide
This is story related. It comes at the end of Chapter 2 when you have been ambushed, just successfully defend your position until a sandstorm comes and opens a hole in the ground which you will fall in.
Story related, cannot be missed. You get this trophy for finishing chapter 2.