4. The Bermuda Triangle
One of the greatest unexplained phenomena of all time, the Bermuda Triangle has gone essentially untouched in the Whoniverse. It is well known that a number of planes and ships have disappeared while in this region and the best (or at least the most entertaining) explanations involve the paranormal. And don't all the best paranormal happenings usually end up involving the Doctor? They sure do. There are many Doctor Who-style things that could be happening in the Bermuda Triangle area that would set up fantastic episodes. But what will happen when the Doctor gets trapped in the current of the triangle? My best guess is that the area is a trap that an alien race have been using to capture human transportation technology for years.... and they have accidentally also abducted a number of humans during their study. But maybe those humans like the new world they're put in, perhaps they are being brainwashed by the aliens to give them the secrets of humanity so this unnamed race can take on the identity of Earth! And maybe all of this is happening on....