V is for Valley of Voe

Although not technically in Oz, the Valley of Voe does appear in an Oz book, so it counts. During the events of Dorothy and the Wizard in Oz, our heroes find themselves in an idyllic underground valley. There is a small village there, but no people to be seen. The people are actually there, but they are simply invisible.

This valley is the only place in the world where the dama-fruit grows. This fruit renders all who eat it invisible. All the people in the Valley of Voe eat it so that they are safe from the marauding bears that roam the valley floor. Of course, since the bears can't see the people to eat them, they eat the dama-fruit too. So the invisible people must be on the lookout for invisible bears, which makes for a rather bizarre stalemate.

Another curious plant grows in this valley that produces a sap which allows anything coated with it to stand on water as if it were solid.