I've been playing around with coding on and off without any real purpose and motivation. But now I think I have found that purpose and that to learn more about Bitcoin and altcoins on a technical level. I want to be able to gauge and find out for myself if a particular project is technically sound as they were meant to be.

I've been learning C++. But I want to also do some practical learning. If I already have the basics of C++, where can I start practicing to understand Bitcoin better aside from learning more C++?

I've seen some "make your own altcoin" threads and I thought that might be a good learning experience, but what else?