Earlier this week I was fortunate enough to visit Bletchley Park in Milton Keynes. Home to the WWII codebreakers and also the National Museum of Computing. It was Britain's main decryption establishment during World War Two. Ciphers and codes of several countries were decrypted including, most importantly, those generated by the German Enigma and Lorenz machines. A truly fascinating place with an amazing history. The guided tour lasted around 1.5 hours and the tour guide was very informative and entertaining!
The National Museum of Computing is also excellent (worryingly much of the equipment on display I remember from my childhood!!). The site is often referred to as the "birthplace of the modern computer" and certainly worth visiting if you work or have an interest in IT.