Fort Brockhurst, Gosport

 

Fort Brockhurst is one of a number of forts built in the 1850's-1860's known as Palmerston Forts.  These were built to protect Portsmouth and its naval base from French invasion.  The moated fort stores a lot of English Heritage's reserve collection from the south of England.  You are free to walk around the fort and go into various rooms including the ablutions and ramparts. 

More information at English Heritage 

The fort is open on the second Saturday of every month from April to September and entry is free.