One of these http://www.thingiverse.com/thing:1639224 (eventually!). Each of the 16 bridge sections will take about 6 hours (I've done 4 ...), and S3D thinks that each of the feet will take 31 hours! Oh, and it's a present, so I'm against the clock!
Epic. I don't know anyone who would appreciate the amount of work that would take that I like enough to do it for.
For my dad's 70th, he's almost as much of a geek as me so he gets it. He got me into programming a Spectrum in the 80s so I think he deserves it!