Portland Castle Overlooks Portland Harbour in Dorset stands one of Henry VIII’s finest coastal forts, built in the early 1540s to protect against French and Spanish invasion. Today it provides a great day out for visitors and its audio tour, included in the admission price tells of the castle’s 450 year history and the part it played in the First and Second World Wars. Portland Castle offers lots to do for families and individual visitors alike, and only 4 miles from Weymouth, this historic adventure can easily be combined with some more contemporary seaside fun.