Terra Cotta: Our bible for this series was "Terra-Cotta Skyline" (the author graciously allowed us to quote from it as desired) and the first thing the we realized after reading it is that there's a LOT more terra cotta in NYC then we thought. It turns out to be the key ingredient in most of our favorite buildings.

Waterworks: At least this year's wet weather means they can all be turned on again! Mostly public fountains and waterfalls, but it could be outdoor art that uses water too. (Warning: subject material not suitable for persons with rabies!)