More than 100 historic windmills and watermills will open their doors this weekend for visitors to explore the heritage of Britain’s mills. The attractions, many of which are usually closed to the public, are opening as part of National Mills Weekend. Since 2010, the Wind and Watermills Society for the Protection of Ancient Buildings has been turning the public’s attention to the importance of restoring and protecting traditional mills. While the need for mills became obsolete in the early 20th century thanks to the introduction of affordable electricity, there was a time when windmills and wa…