Scavenger Hunt Inside One Website

Why?

As a fun game, teaching and marketing device.

How?

Start with the first page. Explain how the game works and give the first lesson. At the end of the lesson give a clue as to what to search for on the site, based on what you have just taught.
They might need to use the sites search (if the found out what to search for), or complete an address (URL) to find the next step. Give small bonuses or prizes on each phase to encourage them.
Anyone (or just the first one) who completes the whole hunt gets a big prize.
The clue to the next step is always based on the last page, and the lessons learned so far.