How will I know when I’ve solved the final puzzle of this challenge?

You will have completed thisĀ challenge when you use the correct password to openĀ 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.