(Check out parts one and two of this report if you haven’t yet seen them.) Following the main museum we visited the Mansion, home during the war to the top brass and, before Bletchley Park’s expansion, the codebreakers. Most of this area was simply rooms filled with props to resemble their state during the war, though the wartime office of chief Commander Dennison has some historical significance: the signing here of a deal for the United Kingdom and United States to share decryption work is said to be the first formal stage of what became known as the ‘special relationship‘ between the two countries.

The Mansion also houses an exhibition on the Imitation Game movie, complete with the set of the bar scene where Alan Turing has his breakthrough of looking for known words in messages, plus a wide range of original props. While this appeared to be a highlight for Cumberbatch fans visiting, I found it a somewhat odd experience wondering how impressed to be by the sight of genuine-but-fake artefacts in a real facility that’s otherwise filled with a combination of real objects and authentic recreations.

We then moved on to several of the huts built and used during the war and now turned into exhibits, starting with one that now has an exhibition about the restoration of Bletchley Park and transformation into a visitor facility: shocking local government officials were at one stage on the verge of bulldozing much of the land for redevelopment. The exhibition contains a range of items found in the walls and roof of one hut during the restoration, including several documents that should have been destroyed but were likely stuffed there by staff as makeshift insulation.

The highlight here was the only two surviving Banbury sheets (pictured), a remarkably low-tech but ingenious tool. They are simply sheets printed with entire rows of each letter. Staff would punch holes (one per column) to correspond to the content of each message. By then overlaying the sheets and looking for spaces where the light shone through, it became far easier to spot repeated patterns which could indicate common terminology between messages, giving a starting point for the Bombe machines to test for likely encryption settings. It’s a reminder, along with the sheer number of pencils on display in the various room recreations, of just how much of the work at Bletchley Park was still done by hand despite the technological breakthroughs.

Another hut housed a bank of Bombe machines; between the simulated noise and the absence of windows (to keep the operation secret from staff who didn’t need to know), it served as illustration of how challenging the conditions were for the all-female staff who would stand continuously during an eight-hour shift. Two further huts were less impressive, with each room filled with props relating to a specific element of the codebreaking operation plus a brief information board.

By this point we had spent five hours at the park and it was now closing time, but fortunately the admission price allows unlimited visits for a year, so we returned for a couple of hours the next day to finish off. We started with two temporary exhibitions in the visitor centre. The first covered codebreaking in the first world war, something that involved simpler encryption but was done almost entirely by hand. The second, sponsored by a leading antivirus software manufacturer, dealt with security and encryption in the 21st century. While I enjoyed some of the interactive exhibits including a survey on the access parents, government and medical staff should have to personal data, I was supremely unimpressed with a screen which asked the visitor to assess the security risk of various objects in an office and on a computer and where the “correct” answer to one question was that opening a PDF file poses no security risk whatsoever.

Finally we visited Hut 8, which contains the wartime office of Alan Turing (filled with relevant props), an unexpected exhibition on the use of pigeons to deliver messages, and a range of interactive exhibits dealing with the different codebreaking techniques. Though crowded, these were genuinely illuminating, with useful demonstrations about probability and linguistic ‘cribbing’ (shown here by a game of Hangman.) One highlight was a demonstration of the Eins catalog. This contained all 17,576 possible encrypted ways to write the word ‘eins’ (German for ‘one’) on a machine such as Enigma, a significant choice as Turing had calculated the word appeared in 90 percent of German message. At one stage staff would use the catalog each day to search for four-letter matching terms in messages in the hope of finding starting points to speed up machine-based decryption.

Even with all this, we still missed out on a couple of exhibits through lack of time, namely a garage full of wartime vehicles and the National Radio Museum, a separate facility included in Bletchley Park’s admission.

Any gripes I’d have about Bletchley Park would be minor: it could use a single starting point exhibit that better overviews the encryption and codebreaking process, and it’s somewhat frustrating to have so much information and background about Colossus, but for the rebuilt computer itself to have a separate admission charge.

That said, I would thoroughly recommend it to any Geeks are Sexy visitor who is ever in the area. It’s a remarkably detailed and comprehensive collection of material and seemed to have something for everyone, from small children who simply like pressing buttons to the most dedicated of hardware enthusiast who gets excited by seeing a display of rotor brush wires. Throw in the computer museum next door and it’s enough to fill an entire weekend of hardcore geekery.