Heritage Open Day: Discover the hidden gem that is Howsham Mill. Situated on a small island in the Yorkshire River Derwent, is the restored 18th century watermill. It was built by the new heir to the Howsham Estate in 1755 as a folly or eye-catcher. It replaced an older building listed in the Domesday Book, which was compiled shortly after the Norman invasion of 1066. The mill has been loving restored and given a new 21st century purpose of generating hydro-electricity. The owner, the Renewable Heritage Trust, provides educational visits for primary school children, and the building is used for a range of other events.