What is cave of doubt on Pokemon Diamond?

There isn't a location in Pokemon Diamond called "Cave of Doubt." It's possible you might be thinking of a different location, or the name might be slightly off.

To help me pinpoint what you might be looking for, could you tell me:

* What are you trying to find in the cave? (e.g., a specific Pokemon, an item, a trainer)

* Where do you think the cave is located? (e.g., a specific region or near a landmark)

* Do you have any other details about the cave? (e.g., its appearance, what's inside)

With more information, I can help you figure out the correct location or answer your question.