They are landmarks across the nation which have stood the test of time, and are a lasting testament to industries from a bygone era.
And windmills and watermills with rich histories dating back hundreds of years are now featured on a new set of stamps.
The Royal Mail said it wanted to celebrate the rich agricultural and industrial heritage of the landmarks.
The stamps feature windmills in Nutley, East Sussex, parts of which date back to the mid-1950s, Woodchurch in Kent, which dates from the early 19th century, and Ballycopeland in County Down, the last surviving example of more than 100 windmills that once stood in the region.
Watermills on the new stamps show Cheddleton Flint Mill in Staffordshire, now managed by an industrial heritage trust, Felin Cochwillan Mill in Gwynedd, close to the Snowdonia National Park, and New Abbey Corn Mill, Dumfries and Galloway, which is maintained by Historic Scotland.
Royal Mail spokesman Philip Parker said: “The windmills and watermills of the UK are much-loved landmarks and reminders of our rich agricultural and industrial heritage.
“We celebrate six of these fascinating structures with new stamps.”
For each of the stamps, Royal Mail will provide a special handstamp on all mail posted in a postbox closest to where the windmill or watermill is located for the next five days.
Windmills became popular in Europe in the 14th century. The total number of wind-powered mills is estimated to have been around 200,000 at its peak in 1850, which is modest compared to some 500,000 waterwheels. Windmills were applied in regions where there was too little water, where rivers freeze and in flat lands where the flow of the river was too slow.