The main 'Bletchley Park' exhibition is good, but it focuses on the human experience of the code breakers. Head around the corner from the car park to the National Museum of Computing (also on the Bletchley Park site) to see more technical exhibitions: they give proper demonstrations of the machines invented at Bletchley, as well as the oldest working computer in the world (which was computing prime numbers when I visited).

https://www.tnmoc.org/

I don't know if they are still in print but Bletchley Park Trust published a great series of monographs on particular aspects of the codebreaking story there. Highly technical, written by specialists, sometimes by people who had worked there. I picked up a load of them when I was there and can recommend.

Definitely enjoy the scenery. I've done Bletchley and the National Cryptologic Museum, the former is in a genuinely beautiful location, especially if you have sun.

They have a neat computer history museum there so make time for that too.

This book, written by the man who created and ran the organization responsible for distributing the decrypted messages to political and military leaders: https://archive.org/details/ultrasecret00wint/

Really shows the extent and impact of this knowledge - they virtually sat at the same table as the Nazi high command.