Fort Nelson is one of three Royal Armouries Museums in the UK. Many thanks for allowing the photography.
Fort Nelson was built in the 1860's and is also known as one of ‘Palmerston’s Follies’ as it was one of a series built along the Coast of the UK in defence of a possible French invasion. The fort faces inland despite having a wonderful view of Portsmouth itself, the threat being seen as encirclement and attack from the north.
Today the museum houses a collection of artillery, guns and cannon from down the ages, see their website above for full details.