I have found at least 2 well hidden but ultimately useless secret areas so far. The first one is on Onkamo Ward, climb the tree near the sign to Mortala Dun and then jump to the left above the cave. There is a rather large hidden room there with no coins or item spawns, rather useless. The second is on Jacob's Climb, to the left of the mailbox is a stone ladder leading down into a rock. This seems to be another hidden spot with no coins or item spawns. I wish these spots had a "wormhole" like the hidden one on Koulato Cluster. For those not familiar, behind the pillar nearest the sign to Kryon Kreep is a hidden ladder, climb up the ladder and jump to the right and you will end up in Ruta Asuncion in Ix, a very handy shortcut. I just wish that the other spots that I have found were as useful.
Has anyone else found any interesting spots?