You've found AN end of the game, that's correct :3
I don't quite remember everything that's accessible, but if I remember correctly... working with Bass lets you reach an area called the Deep Cave. Just exploring the path towards the bottom of the mountain (getting as far down as possible in the village, then get to another outside section, then further down) lets you get to an area called something along the line of "Abandoned Construction Site", though I probably used a different wording. Both of those lets you progress down different story paths.