This is part of the National Museum of the Royal Navy and we had one of the ultimate explorer tickets which allows entry to all the parts of the museum based in Portsmouth. This is one of two in Gosport (the other being the submarine museum). You can drive (it has a large car park) get the waterbus from the main museum in Portsmouth (which is also included in the ticket but the times are quite limiting) or do as we did and get the Gosport ferry across from. Portsmouth and walk (about 15 - 20 minutes). We visited mid afternoon and it was quite quiet when we visited.
The museum is the old naval munitions area and it tells the story of how gunpowder and weapons were used on ships and how they were made at Priddy's Hard (the old name for the area). It is set out in an interesting way and there are interactive displays including stories from people who worked there or used the weapons. It is really interesting and we spent just over an hour and a half looking round.
One of the highlights is the amazing Camber cafe at the end of the visit which does a range of snacks, cakes and drinks. It has a large indoor seating area, but if it is dry then there are outdoor tables which give a great view of the harbour. It is also good value with large slices of cake for under £3 (they are almost double in the main dockyard)
Being in Gosport it is perhaps overlooked by those wanting to see Victory and the Mary Rose, but a little effort to get here will be rewarded with a interesting visit and some very friendly and helpful staff!