I visited Bletchley Park museum this summer when in London. Can recommend and it's also really easy to get there; just a 50 minute train ride from London Euston station, and 5 minute walk to the museum. Entire family enjoyed the museum (have two teenage kids). There is also the "National Museum of Computing" located next to it which contains the Bombe, Collosus and related equipment. As I understand it most (or all?) of the original hardware was destroyed after the war to avoid leaking any information about the British code breaking skills. Thus, the machines on display are replicas, but should be fully working.

The computer museum also exhibits post-war computers all the way to modern machines. I'd say that museum is more for the geeks while the Bletchley Park museum is definitely worth a visit even if you're not into computers.

A personal Bletchley Park anecdote: my grandfather, an electrical engineer, staffed a radio listening station during the war, and every evening a motorcycle dispatch rider would take the day’s intercepts away to a secret location. It was more than 20 years before my grandfather figured out they went to Bletchley.

In the 1980s the Bletchley museum project put out a call for wartime electrical components so they could build their Colossus replica. My grandfather in the 1950s had made a chain of Christmas tree lights from govt issue tiny light lightbulbs he pinched from work. He painstakingly removed the nail polish he had painted them with 30 years earlier, and sent them to Bletchley. They used his family Christmas lightbulbs in the replica that is still there today.

I had the privilege of touring the museum with him in the 1990s. Also on that day I heard my grandmother’s stories of her time in the British Army during the war. That day was incredibly interesting and moving, and is an important memory for me.

I recall from my own visit that the electrical transformers are supposedly original. So, the National Museum of Computing justifies calling its Colossus a rebuild rather than a replica, since it is made with some original parts.