There is a group of logs standing in front of the cave's entrance that you can't fit between. I've tried bashing them with my weapons, and I've even tried lighting them on fire to see if they would burn down. Nothing seems to work. I don't know what YOU are talking about. Clearly, not all Unknown Locations are, "perfectly accessible".
Usage: Build village huts, craft weapons and items. Rare South Maple . Location: Rarely while collecting the South Maple. Usage: Build huts and upgrade weapons. South Stone . Location: Southern edge of Oros. Usage: Build village huts, craft weapons and items. Rare South Stone . Location: Rarely while collecting the South Stone.