all great suggestions but i would also like to add set up virtual machines with solaris and BSD. Also, some flavor of linux that you like. perhaps gentoo? that will keep you busy for a while.

then get them to do remote displays, ssh, learn the disk structures, useradd, usermod...etc. I switched a few years ago and love it. its quite the learning curve and fortunately i have a lot of unix machines here, especially Sun machines and a mock up of everything in a testbed. so i can break all i want and have to learn to fix it on my own. Its a hair pulling and frustrating event but the more you know the better off you are. it gets easier as you go along, what you thought was difficult a few weeks ago is now easy.

good luck!