I first discovered this on another 365-days-project blog. (He's making stars as well! :D) The original design and instructions are by George Hart. What can I say: I immediately fell in love with the idea and the design and had to try it myself.
It's a bit of a tricky one and when I held the first three cards (of twelve total) in my hands, I honestly thought it impossible. But eventually, it took only a little over an hour to make this:
If you ever want to feel really good: Try this - and don't give up! It feels fantastic when the final card slips into place! :D
Here's a shot of the interior I took before inserting the last three cards:
P.S.: 24 spikes.^^