Someone else took down their guide. but this is just for reference. the previous guide stated he wasn't sure on how many. but he said he got the achievement on 3. from what i can tell there is 3 possible camp sites on the map. now be careful with the edit option. you can void this achievement if you replace an island that had one. you don't need to pick up anything. you just need to walk inside their campsites. 1st was a flipped boat. 2nd was a crappy wooden hut. and the 3rd was a stone hut. they all contain at least 1-2 skeletons inside.hope this helps out those are are curious.