They are all still free which is a rarity today. You need a full day for the Imperial War museum as there is just so much to see. Unfortunately I think you have to pay for this one but it is worth it. When I was over in France there was a great one at Eperleques which houses the V2 Rocket sites and they did the space race between Russia and the States concentrating on the German scientists who were involved. What amazed me was it belonged to a farmer who then handed it over to the Government as it was too important and most likely expensive to do properly.