The most delightful object in Cottered church is a mural of St Christopher. Almost every church (in England at least) once had one, prominently positioned opposite the main door (usually the south) so it would be the first thing you saw as you entered, and could be glimpsed from outside. This was because it was believed that to see an image of this saint protected you from dying without the proper rites of the Church on that day. There are still getting on for two hundred medieval paintings of Christopher, far more than of any other saint, in the country, though they're in various states of preservation. (There's another good one in Newnham.)
The saint's legend tells that he was an unusually tall Canaanite, and a recent convert to Christianity, who decided to be of service by helping travellers cross a river. One day he carried a child on his shoulders across the deep and fast-flowing river, who seemed to become so heavy that he feared for their lives. When he finally reached the other side he said to the child that it felt as if he had been carrying the weight of the whole world. The child replied 'You had on your shoulders not only the whole world but Him who made it. I am Christ your king, whom you are serving by this work,' and vanished. This is just the sort of fairy-tale-like, uplifting, feelgood story beloved by medieval Christians. It's not hard to see how he became the patron saint of travellers.
In Cottered's example, which dates from the 15th century and was rediscovered under layers of whitewash in 1886, the figures of Christopher (which means 'Christ bearer') and Christ are faded to bare outlines, but fortunately the background is quite well preserved (though I think it has deteriorated and lost some of its finer detail since I first saw it in the 90s). It depicts a bird's-eye view of a schematised countryside with zigzagging roads, trees, hedgerows or fences delineating fields and the edge of roads or paths, numerous buildings (mostly large high status ones, because ordinary dwellings were presumably thought less worthy of inclusion) and occasional inhabitants. It amounts to an idealised version of a typical north east Hertfordshire landscape. A detailed description, starting top left and working down, and then the same for the right, follows.