Mystery Photo #80 Posted on July 11, 2012 by boscovstravel Here’s how it works: we post an image and provide a clue. Leave a comment with your guess. Good luck! Hint: This site is the largest Roman city gate north of the Alps. Photo courtesy of Avalon Waterways. About these ads Share this:PinterestFacebookTwitterTumblrGoogle +1StumbleUponDiggRedditEmailLike this:Like Loading...