Rails is known as a productive platform to serve your Ruby application, and at the same time, Rails is a very well written piece of Ruby code. The whole framework is written in the same language as the one you use to compose your apps, and everything is open-sourced. There's no secret. It's just Ruby.
This talk encourages you to step into the Rails code base. Through this talk, you probably will get to know:
How Rails boots
How Rails loads itself, libraries, and your application
How Rails handles requests
How Rails interacts with databases
How to read Rails
How to debug Rails
How to patch Rails
How to extend Rails
After attending this talk, you will find that the framework is no more a black box for you.