phantaphreaks

Best answer as chosen by Asker / Ratings
From what I can tell I think you have to survive long enough to complete the picture book to unlock the option to play without your partner. Beach three is in the third area, after you go over the stepping stones to beach 2, all the way in the upper left corner of your map there will be two notches that look like they lead somewhere else, one of them has a boulder in front of it, take your partner, push it over, and it will take you back to your cave, little cutscene and you can go back, there is a fresh water spring right inside the door, and out the other side is the next area and beach 3. Check your map always if you get stuck.