There's a very similar question that refers in the title to RouteDebugger, but really they were using Glimpse, and the actual title question was never answered.
So here it is again specific to RouteDebugger:
If I'm getting a 404 in MVC3, how can I debug that route and the resulting 404? RouteDebugger doesn't appear for these results, and while MVC source code is available, the Routing engine's source code does not appear to be available, so there's no apparent way to step into the code and see where exactly things are going awry.
Is there a way to get RouteDebugger to work on 404 pages, or a way to step into the code from beginning of request through to MVC Controller responding?