The fact that the dark side of the moon is always facing away from the earth it is still very easy to be a base there that we have not seen or know about. This is why we need to get a base up there so we can explore more of the surface of the moon and not just the parts we can see.
As far as I know we have not explored it and probes are unreliable at the best of times.
I also believe we need to check some of the stuff in our own waters too. Take a look at this. Source 6u.