S.T.A.L.K.E.R.: Shadow of Chornobyl

In Agroprom Research Institute in NW corner is a bog. When you approach it beware of high radiation and make a save. What also happens is you'll hear lamenting.

When you go deeper into the bog you'll see a train cart. Inside is a friendly Military. The soldier is a deserter from the faction. Finding him will reward you with the achievement.

There should be some artifacts around, but otherwise you'll get nothing out of there so you might as well reload.