I received this achievement right after the prologue, while I was en route to the safe house. Any time you see a "?" on your mini-map, just get out and investigate. Sometimes you will have to follow a trail and find a few clues, or you may just have to open one box. All three of these achievements should come naturally with a bit of exploring. There are way more than 20 point of interest. It should also be noted that one playthrough means one save file. You can complete the storyline and still go back and get the rest of the achievements within the same savefile.