Garrison Point Fort

Garrison Point Fort is a former artillery fort situated at the end of the Garrison Point peninsula at Sheerness on the Isle of Sheppey in Kent. Built in the 1860s in response to concerns about a possible French invasion, it was the last in a series of artillery batteries that had existed on the site since the mid-16th century. The fort's position enabled it to guard the strategic point where the River Medway meets the Thames. It is a rare example of a two-tiered casemated fort – one of only two of that era in the country – with a design that is otherwise similar to that of several of the other forts along the lower Thames. It remained operational until 1956 and is now used by the Sheerness Docks as a port installation.

Source: Wikipedia