This achievement is story related and will be awarded after completion of the mission "Payback". This mission is a little confusing with things you have to do so I will try to explain it my best. This is one of the typical far cry franchise's hallucinogenic missions.
You first have to travel to the abandoned Keo mine up in the mountains of North Kyrat. Now enter the cave. On your left there will be a hole in the wall. Walk through this and there is a letter laying on one of the boxes inside that room. After the cut scene ends, follow the blood trail to the very end of the river. Look up. There will be a grapple. Climb up the wall, kill the soldiers in the area below, and destroy the gate. To destroy the gate shoot the flaming pots on the other side of the gate with your bow and it'll blow up. Now do some more grappling across the ledges. you will know you're in the right area when you do an immediate grapple after grapple 5 or 6 times in a row. In the next area, you will have to kill Kalinga 3 times as well as some more soldiers and a white tiger. After you kill him the third time a cut scene will start and you'll be back in the original cave and the achievement will pop.
if anyone has any questions let me know.
-Fr3aK