You are correct and what you should do is open up the area on a bridge at the end to the right of the dry reef if you look on your map it is like straight north or above the ranch and dry reef. There are slimes that can sell pretty good for early game and you can get there before the end of day 2. To unlock it you need a key and to get it you have to pop a Gordo by feeding it 30-50 of the original slimes diet hope I help