The hidden black bat cave room you can only tele into
There was only one thing in there, and that was a vampire bat even though it wasn't new moon. No gold was in the room. Nothing at all.
We were able to find out where the hidden room was using detect metals. This method was inspired by Squidbit. The room is near the entrance. If you walked in the bad cave and went straight, and were able to go through walls, you would go through the hidden room or come very near to it.
With the evidence we have we were able to infer that this is where the hidden room is.