Escher's "Relativity" in LEGO

Y'know, sometimes I like to complain to my friends that I have too much free time. What's even worse is the fact that I don't really accomplish much in these copious amounts of free time.

Now here's a story that puts me to shame: Andrew Lipson, computer programmer, has a job that keeps him away from home for over 75 hours a week, and yet he still finds the time to create things like, for example, Escher's "Relativity" in LEGO.