This is not too difficult, but missable. You can get this achievement in the adventurer's puzzle. Right after you got into the pyramid, you go right, up the second ladder (first one leads to the Sarcophagus) and there is a picture of three egyptians ... walking like an egyptian. So basically, all you have to do is to assemble all your three characters in front of this picture and you're good to go! Achievement unlocked ;)