I would highly recommend Michael C. Feathers' 'Working effectively with legacy code' to anyone who cares about code, how it is written and how to deal with complex and (automated) untested systems.
Although the word legacy might evoke images of Fortran or COBOL procedures, the definition in the book refers to any kind of system that does not have an automated suite of test to rely on when making changes.
It was in this book where I read about the concept of telling the story of the system. According to the author, you need at least two people for this technique to be effective. One asks the other; What is the Architecture of the system?
The other will answer the question in just a couple of sentences, using only a few concepts, and targeting individuals with no prior knowledge on the system itself.
So I asked Jon Kaplan if he'd be so kind to put this into practice with Open Wonderland and this is the result: