This card opens out, and out, and out, and out, and back to the beginning again for ever. I made one for DH's godson's 12th birthday and he liked it so much that I made another one for our nephew's 12th. OK that's not till next July but you can never be too early, and meanwhile I can play with it... ;)
ETA: I've added the template that I used as inspiration to make this card. For visual instructions, search for "infinity card" or "everlasting card" on Youtube. There are some really good videos.