The clue is nothing more than a single English word. It will be clearly marked as such at the bottom of the solution pages for each of the first seven puzzles.
You will have completed this challenge when you use the correct password to open a page whose title says that it’s the final page of the challenge. That page will contain a big congratulatory message on it, the tracking code you’ll need for the travel bug, and other surprises. There’s really no way to miss it – if you’re not certain that you’re done, you’re not done.
At least seven.
The place where the final benchmark was located was destroyed. The container was hidden deteriorated to the point where the container was completely exposed to muggles. The log book and contents have disappeared. Consequently, the final has been archived.