Completely unique and always fascinating, the Wellcome Trust, not far from the British Library, is a free museum devoted to the marvels of the human body. It has regular exhibitions, taking sideways scientific looks at everything from the the anatomy of the brain to the secrets of sleep (and the recent exhibition on death was not remotely as morbid as it sounds). But it's worth a visit any time for its permanent collection, which combines clever hands-on exhibits that teach you about your own body with thoughtful artworks that reflect on the human condition. Also has a great cafe and bookshop. And I learned where my pancreas was for the first time. Who knew it was halfway up your back?!