The 'mill' is actually an elevator. Take it up, climb a few ladders and you'll happen upon another stone elevator (you should find a key nearby on the way). This will take you to the valley of drakes. Crossing a nearby bridge will lead you to a stairway which takes you to New Londo, immediately therein you will find another stone elevator to Firelink.
For she doted upon their paramours, whose flesh is as the flesh of asses, and whose issue is like the issue of horses. - Ezekiel 23:20