Geograph - photograph every grid square

Twin round kiln oast house.

Grade II listed.

A National Trust is an organization dedicated to preserving the cultural or environmental treasures of a particular geographic region. They generally operate as private non-profit organizations, although some receive considerable support from their national government. The first such organization was the National Trust for Places of Historic Interest or Natural Beauty, which is the National Trust of England, Wales and Northern Ireland, formed in 1895 and operating as a charitable organisation.

Extract from Wikipedia Link

List of National Trust places Link

Grade I listed buildings and structures are of exceptional, even international importance. There are over 6,000 in the country. Only 2.5% of listed buildings are Grade I listed.
In Scotland the classification is Category A
Index: Link

In the United Kingdom, a scheduled monument is a 'nationally important' archaeological site or historic building, given protection against unauthorised change.
There are about 20,000 scheduled monuments in England representing about 37,000 heritage assets. Of the tens of thousands of scheduled monuments in the UK, most are inconspicuous archaeological sites, but some are large ruins.
Wikipedia: Link