The Congress for the New Urbanism (CNU) – probably the most significant urban design movement in North America since Levittown and the rise of suburbia – turned 20 in West Palm Beach last week. CNU20 was my first congress, and it was by turns amazing, amusing and a bit dull, and overall it’s probably the most important conference I’ve attended since this convergence-of-climate-change-and-energy-scarcity thing I went to in 2006. Let me explain why.