Setting up an old PC with linux and just not installing a GUI as already suggested might be a fun project to do together and exploring various command line programs (maybe ncurses based programs like mc, ncdu, etc.) and I just read about a cute text adventure called bashcrawl which teaches unix commands as you play (“cd” into a room, “ls” to show the items there, etc.). There are so many bash programs (and games) like gnugo and chess that are interactive but without a GUI. Here was where I read about bashcrawl (I haven’t tried this myself): opensource.com/…/learn-bash-command-line-games