Ken Jennings — yes, the well-known Jeopardy! champ — is collaborating with Smithsonian magazine on “The Great American History Puzzle.” This great big puzzle hunt will begin in the October issue of the magazine (you can download a free PDF here) and then leap out on to the Internet: Solving the codes and puzzles in the magazine will get you the password you’ll need to access this Web site. On October 1st, the first of ten challenging puzzles will appear on the site. Save your answers to the first nine puzzles — you’ll need them for the big finish. The first person to e-mail the correct answer to that final puzzle (it will be available on October 22nd) will win a trip for four people to Washington, D.C. plus a behind-the-scenes tour of the Smithsonian.

Serious solvers will want to keep an eye on the contest page — Ken will be blogging there, and might just offer a hint or two as the contest progresses. And just in general I highly recommend Ken’s own excellent blog.