The Imperial War Museum North is located by the water of Salford Quays, close to Manchester. It is easily accessible by bus or tram, or if you are coming from further away they do have plenty of space to park. Entrance is completely free, there is the option to buy the guide book or make a donation towards the running of the museum.
The theme is obviously 'War' but more specifically the museums exhibits focus on the world wars, with smaller exhibits for other historic conflicts. There are plenty of objects of interest, weapons, clothing, tanks, planes etc. There are also some interactive exhibits to get you involved in the sights and smells of war.
Really good way to spend an afternoon, not enough to keep you busy for any longer than that.