Good times were had on an old server with just leaving an unlabeled Mystcraft portal deep in the base next to something I wanted protected (the MFFS control room). Noobs exploring the base *had* to discover what was in it.
Like flies to honey, heh.
The actual trap was mostly harmless; just an endless desert with a wireless tracker on the landing point. However, a lot of people don't carry linking books to escape so this was really pretty evil.