The Mansion at Bletchley Park. Though this is the most photogenic building (and oft-used when Bletchley Park is discussed), not much actual code-breaking work went on there.
Also, the weather was rainy and miserable when I was there, giving a far more accurate representation of what it's normally like than the sunny pictures you'll see elsewhere on the Web (it is Britain, after all).
One you're out of the ticket building (which, next to the main entrance, is actually a little bit away from the Mansion), you begin a cleverly-designed guided tour. You're given a heavily-protected iPod touch, which has a video explanation for each area, plus additional videos, interviews, and photos which add to the experience. It worked really well.
One of the lovely rooms inside the Mansion. Before the huts were built to accommodate the ever-growing staff, this room housed German and Italian Navy code/cipher breakers. Later it was home to a typing pool.
I thought this was a neat touch. The ballroom you saw in the previous slide was an addition long before the war. Here you can see one of the original exterior windows. A movie projector was set up roughly where I'm standing, and projected through a hole where the window was, to be viewed in the ballroom.
The back of the Mansion. There used to be a wireless receiver at the top of the tower (center, distant), but they realized this would make the building conspicuous, so they removed it early on in the war.
I tried to decode what special significance the truck's lettering held, but failed.
From Hut 11 you get to walk through Huts 3 and 6. They've set the rooms up to appear roughly as they did during WWII, including blackout shades that do wonders for ambiance, and do make photography a challenge.
Though the Bombe machines (and their successors) helped a tremendous amount, much of the code/cipher breaking was still done by people, with pencils and paper. Here you can see one of the crossword-puzzle-lookalikes that many used.
Each group of three (stacked vertically) functions as it's own Enigma machine. The top rotor spins rapidly, and at each full rotation, the rotor below clicks one letter over, when that one finishes its rotation, the one below it clicks over one letter. This goes through every permutation of the starting position of the encoding Enigma possible, in about 12.5 minutes.
This is only part of the whole process of reading enciphered transmissions, but the Bombes sped up the process significantly.
Since it would be decades before anyone who worked at Bletchley Park could talk about it, the British Government built a memorial to their service, estimated to have taken more than two years off the length of the war.
Check out more, and get info about taking a visit yourself, at the Bletchley Park website. It's just a hour outside London by train, and well worth the visit.