The twelve Zodiacs are at the following locations:
-In the swamp after completing the bridge. -In the swamp in the well. -In the swamp behind the chatty spider. -In the bush in the Fuzzle field. -On the raft after you rebuild it. -On the other side of the stone bridge at the first ruins). -On the other side of the stone bridge at the observatory ruins). -On the side of the cliff by the observatory. -From the old man in the ice. -From the large face statue to the left of the old man's cave. -In the tree protected by the bees. -In the pond that you get from the big fish.
The key is hidden in the ruins on the left side of the land, after building the stone bridge to cross the river. Across the river is one set of ruins, then to the left and south of that is a big briar patch that needs to be removed. Once done, cut down the large dead tree to get across the chasm to the last area. The ruins of the observatory are in this area. Once your workers clear that area, the Libra Key will appear.