I had a really great professor in a class I really liked. I went to his office hours towards registration time for next semester and asked about an individual/independent study course. He was open to it and even fought for it to count towards something I needed to graduate.
It was so liberating to chase my wild ideas down their various rabbit holes and do legit research. I wasn’t, and likely won’t be a phd, bs in engineering was enough for me, but it was a nice break from the norm