Time travel book can't remember the title

As a teenager on summer vacation at my grandparent's cabin in Norway I read a book about time-travel. No one went back for ten years. I looked forward to finding the book when I finally returned but the mice had gotten to it and it had already been thrown out. Someone please help: all I can remember is that it involved time travel, medieval Europe (most likely England), and the key detail: there was a magical ford (as in a shallow river crossing). It was either magical or somehow significant to the plot. Thanks a bundle.