> I'm really looking to _build_ something rather than just going through a book or tutorial (although they have a place and time). '
It might be worthwhile to start 'small' by taking one of your C# projects and converting some small section into a native/unmanaged C or C++ DLL that gets used by the C# side. There's a lot of boilerplate involved setting things up on both sides of the divide, but you can stay in a mostly familiar environment yet start learning about some of the 'magic' C# handles for you that is exposed by the unmanaged code, and extend your experimental forays into the C side as you get more comfortable.
It might be worthwhile to start 'small' by taking one of your C# projects and converting some small section into a native/unmanaged C or C++ DLL that gets used by the C# side. There's a lot of boilerplate involved setting things up on both sides of the divide, but you can stay in a mostly familiar environment yet start learning about some of the 'magic' C# handles for you that is exposed by the unmanaged code, and extend your experimental forays into the C side as you get more comfortable.