5. Upside-Down Land
This one is inspired by a favourite childhood story of mine - Enid Blyton's "The Magic Faraway Tree". In a story which I vividly remember for its hilarity, the main characters end up in "The Land of Topsy-Turvy" and are forced to walk on their hands for their entire visit, or risk reprimand from the Topsy Turvy police. The Doctor, in all his childish enthusiasm, would probably embrace this land with rapture and cheerily greet everyone he comes across. However, I can't imagine Clara (or any other companion for that matter) being too impressed with the destination! It would create scope for a lot of laughter - particularly for one of the lighter episodes of which Moffat has been fond of late. As the fourth Doctor said, "There's no point being grown-up if you can't be childish sometimes".