My personal pilgrimage seems to always end up designing designing a stack virtual machine and writing a compiler for it for a toy programming language. I tend to pick this up every time I learn a new language to get a feel for it.

I usually get it to run a simple loop to print hello world and do the inevitable Fibonacci generator and get bored. No fancy things like functions!

One of these things was crudely repurposed into a domain specific language for a job as well which was handy.