I've always been interested in making things that make other things, and compilers definitely fall into that category.
In the middle of the second assignment, the parser. It's a lot to consume, but I feel like the theory isn't particularly difficult, about half my learning has been getting to know the tools (so far: flex, bison). I've also spent an annoying amount of time on updating and configuring the VM, I guess that's a bonus lesson in Linux sysadmin-ing. It's also my first experience with C++, which seems useful to know.
I also started this course on web security: https://web.stanford.edu/class/cs253/. The first assignment was a lot of fun, the material is fresh, and it definitely seems like very useful information for anyone in the web stack.
I'm also learning a bunch of new cooking recipes, but who isn't nowadays.