Bridge of Birds.

This the first of three books in the "Master Li and Number Ten Ox" series, and it won the World Fantasy Award in 1985. Set in "an ancient China that never was", it's the story of a young peasant man who's as strong as an ox, and an ancient sage with a slight flaw in his character. It draws on Chinese folk tales and history, as well as a bit of Sherlock Holmes. It's a mystery with magic, humor, adventure, and it's simply mind-blowing.

This one one of those books that people ask to borrow and never return.