There are two ways to get to Hurst Castle. You can either trek along the shingle storm beach from Milford-on-Sea, or catch the ferry from Keyhaven.
Suffice it to say that walking any distance on shingle is not my idea of fun.
Whichever way you get there, you find yourself on the end of a spit of land that sticks so far out into the Solent that the Isle of Wight seems almost in touching distance.
The strategic importance of this site in guarding the western approaches to Portsmouth and Southampton from the pesky French is immediately obvious, and there are remains on the site from three periods when the threat of invasion was felt to be very real.
The core of the castle was built by Henry VIII in 1541-1544 as one of the Device Forts, and was once used as a prison for Charles I. On either side of this are two enormous Victorian wings built in the 1860s to house a total of 30 heavy guns of varying calibers. This may seem excessive, but you have remember that each gun took about three minutes to reload, and would probably, therefore, only get one shot at any enemy ship.
The final threat was from the Germans during the last war, and a number WWII lookouts and gun emplacements were built on the roofs of the old buildings.
Check the English Heritage website for opening times etc.