From "Along the Road" 1925, a series of essays by Aldous Huxley..
"And when at last one has arrived at San Sepolcro, what is there to be seen? A little town surrounded by walls, set in a broad flat valley between hills; some fine renaissance palaces with pretty balconies of wrought iron; a not very interesting church, and finally, the best picture in the world." Resurrection
How to top that? Well there was a minor battle in the fifteenth century in the valley between Sansepolcro and Anghiari which was to be commemorated by a painting by Leonardo da Vinci in the Palazzo Vecchio in Florence. This is a famous lost painting, mostly known from preparatory studies. Battle of Anghiari
Sansepolcro has much more to offer (and the Duomo has some interesting art, despite what Aldous Huxley wrote). It is a prosperous small town with good restaurants and small shops, possibly with too many clothes shops. It is at its best on a warm summer evening when the whole town seems to be out on a "passeggiata" - teenagers strolling up and down the main street - and so are their parents and grandparents. Sansepolcro
Also for the many accountants who come to this site, Sansepolcro was the birthplace of Luca Pacioli who first described modern accounting practices. He was also a friend of Leonardo da Vinci (all above references are to Wikipedia).