One of the pixies in the village tells you that there's a pixie village beneath the Infinite Darkness. What he says may be essentially true, though I haven't gone through it to actually find the end. It is, by all appearances, the most difficult part of the game.
It isn't on the map. It's actually below the map. It's below where you find the pixie at 38,29, which is on the bottommost part of the map towards the right, in an area that you drop from above and can go left and right (the pixie is on the right end) - look behind the pixie on the ground. As I said above, it is an absurdly difficult challenge. Also, some of the lightbeams are there, so if you're having trouble collecting all 60, keep in mind that some of them aren't even on the map. So there.