I think this idea for a Save the Date is a lot of fun. If you want something that people haven't done before, and your guests to be wow'd...definitely send them a postcard with all the details for your special day.
The best way to describe these invitations is actually in the words of the bride. The bride, explains, "I knew that I wanted our wedding invitations to be something that our friends and family would remember and hold on to, long after the wedding. They are both highly adventurous people - they love traveling, discovering new foods, going to markets, meeting new people and exploring the world with all of their senses.