Visual representation of the parts of a Rails application

I've been learning Rails for a few months now and recently realised it would be convenient if there existed some visual "map" of the parts of a Rails application. Not just the MVC parts but more nuclear bits such as partials, specs etc. This might be illustrated as several flows e.g. when a page loads and when a test is run.

Does anything like this exist?

Have you taken a look at the source code? It is well written and commented and you should be able to gain some understanding from it. Here is the code for the 3.0.9 branch https://github.com/rails/rails/tree/3-0-9

As far as visualizing your own application goes take a look at Rails ERD or Railroad