The barrier past the mine (and across the water) can not be disabled until after you have the battle tower. There are a couple sections of beach you can get to by swimming, one with level 18 or 19 black ring members (by some anti-dragon weapons you'll deal with later), and one with level 21 imps (and a mine).
Prima had the guide on their site, then pulled it and put up a message that it was 'coming soon', then canceled it completely.
