Where is the mysterious cave located because I don’t see that on the world map and I’ve explored everywhere?

Where on the world map is the mysterious cave because I’ve explored everywhere and haven’t seen a place called mysterious cave?

Can someone please help me find the Satori Book? I have been looking for a while now. I know some people are saying the mysterious cave? Is this actually the mysterious forest? Because I have searched there for a long time. Please help?

Can someone please help me find the Satori Book? I have been looking for a while now. I know some people are saying the mysterious cave? Is this actually the mysterious forest? Because I have searched there for a long time. Please help?