How often do you walk past a crumbling building and never even notice? Actually, that's a pretty lousy question since you never notice.

A better question would be how often do you walk past a crumbling building and never even notice, even though it's been repaired with freaking LEGOs?!

The answer to that, for me at least, is probably pretty often, as it took me two weeks to realize German artist Jan Vormann had come to NYC.

As part of his international Dispatchwork art project, Vormonn patched up some buildings in well-traveled areas (Herald Square, Bryant Park, Times Square, etc.), just as he'd done previously in locales such as Berlin, Amsterdam and Bocchignano, Italy (pictured).

Intrigued by the idea of custom-made LEGO wall patches, it was obvious I had to find them, and using the addresses given on his Web site, I set out in search of some public art.

Sadly, most had already been removed by the time I got there. Except for one that had apparently been sentenced to a fate worse than death -- to linger around the base of a Roy Rogers across the street from Penn Station for an unknown period of time.

Slightly miffed by the fact that my only photo op required me to crawl on the sidewalk across from Madison Square Garden (NOTE: if you plan to do this, try not to lose your hairbrush three days prior -- you will be mistaken for an extremely crazy homeless person), I wrote the artist to find out what the life expectancy is of these LEGO installations.

He said, "I guess they stay up about a week or two, depending on the spaces. Maybe even only a day or some hours. But it is all right, I think. Shall it be used to play more -- right?"

It's true. I had been tempted to pick up a few of the pieces that had fallen onto the ground to put on my shelf of random objects I keep for the day I finally make my audition tape for "Hoarders," but I resisted, thinking maybe a kid who could actually have fun with a dozen LEGOs would enjoy it more. Or a pigeon hell-bent on making the most awesome nest in history. Hopefully those are the kinds of people (and animals) responsible for the LEGO installations' rather short lives.

But nobody really knows who's responsible for taking them down, and their continuing (or not) existence is something of a mystery even to Vormann, who leaves town before his art does.

He says, "I get feedback from people a lot who tell me that here and there, they are gone, and it is sad. But you know, it can be seen as a temporary thing, a performance, which stays in this world for some days, on pictures and the memories of people who saw it even longer!"

Although my day could have been categorized as something of a bust by some, scouring the city and looking for almost-secret public art was a lot of fun, and the ability to waste a lovely afternoon doing so is what makes living in a city so great. Even when it means totally humiliating yourself in front of a Roy Rogers.

Emerald Catron is freelance writer who could destroy you at "Super Mario Bros. 3."