This is an incredibly fun and creative idea for a Save the Date.
"After ten years together, Jen + Kevin got engaged in Paris – a location they subtly acknowledged in a nod to Albert Lamorisse’s short film The Red Balloon when designing their save the date announcement. Wanting to treat their wedding as a big party more so than a traditional event, each guest received a deflated, red balloon tied to a letterpress printed card reading: “Hello! Please inflate the balloon.” Once inflated, the piece reveals all relevant information and sets the desired tone with humor and playfulness."
Photo credit: http://www.underconsideration.com/