The trick to sysadminning is doing the most with the least amount of home-written code. That’s how you make it a fun challenge. Anyone can brute force a problem. The skill– and the fun– is in solving it with style.

Sysadmin Thought Challenge –
Here’s a theoretical problem. How do you solve it?
“Let’s say you have 500 machines, and 5000 users. How do you do authentication?”

Why not take it a step farther? Heck, set up challenges, and provide the machines (UMLs) to do them.