The National Museum of Computing is on the grounds of Bletchley Park. It’s a rather unimposing structure and was, unfortunately, mostly closed. You could get into a portion of it though and see some of the code breaking equipment and the replica of Colossus, the first electronic digital computer. This computer was used to break the German Lorenz coding machine. It’s pretty impressive and must have felt like a furnace when it was turned on. The last few pictures in the set Colossus.