How to create the perfect 404 page

There is nothing more frustrating than landing on a broken webpage and seeing the below message, in fact it's one of my biggest bugbears. This is what users see when they land on a page that doesn't exist and has been deleted or the URL has been misspelt. As you can see from the image below the generic 404 page is pretty useless and doesn't even attempt to help users continue their journey to your website. Guess what users do in these situations?...