New York City's subway grates got an ingenious dressing up in 2008 by an artist who made inflatable sculptures. His media were plastic bags, tape and the upward rush of air caused by subway trains passing underneath the city streets. The process of deflation and eventual "death" was just as interesting as inflation. I've placemarked a subway grate. Of course, it's not necessarily one Joshua graced with his delightful creations, but having an idea of his exhibition environment makes his artwork seem an even more whimsical process.
Go to his website for a charming video of people reacting to his inflatables: HERE. I could not find recent examples of any work besides his photography, so it does not seem that Harris continued his inflatables after 2008. No doubt there are some New Yorkers who miss them.