The Isle of Grain is found in Kent at the tip of the Hoo peninsula. It is no longer an island and is now mainly marshland. The main feature of interest is a Napoleonic fort about a quarter of a mile off the shore which can be reached by a crumbling causeway at low tide. The fort was originally a Martello tower but extra barracks were built adjacent to the structure later. The tower served as an artillery fort until the 1950s, protecting the mouth of the River Medway and in the First World War anti submarine nets were strung across the River Medway and attached at one end to it. You can still see the heavy chain which held the netting, wrapped around the tower.