Topic: Submarine
Gosport Submarine Museum, 2002
A fun day geeking out over Navy tech, including going inside an actual submarine (HMS Alliance).
Bletchley Park, 2001
Celebrating the release of Enigma, the film based on Robert Harris's novel. He was there signing autographs, and Simon Singh, author of The Code Book, gave a talk about cryptography.
There were a number of people in costume, and there was even a collection of props from the movie scattered around the grounds, including a realistic-looking submarine conning tower sitting in a car park.