I'm watching the Doctor Who episode "The Pandorica Opens" and I noticed a few things wrong.

Q1.) Wasn't the Doctor there when Stonehenge was built? If so, why didn't he know about the Pandorica being buried under it?
A1.) Yes, but it was in a novel and might not be considered cannon. And even if it is, it is possible that it was buried before he got there.

Q2.) Why did River say no one knew how old it was when The Monk had been there when it was completed?
A2.) She didn't know about that? The Doctor might have mentioned it, but he was a bit more concerned about the T.A.R.D.I.S. being destroyed at the time.

Q3.) Why hasn't any one found a staircase or anything under Stonehenge before afte all the research that has gone on there?
A3.) Maybe there is a Perception Filter covering all that.

Q4.) Why did they not notice a Cyberman head not far from the staircase?
A.) um. a perception filer? Not sure why. Maybe they just didn't explore that part before they found the staircase.