What on earth (or beneath it) is going on at the corner of 60th Street and Fifth Avenue? Fret not. The "building" now protruding from the sidewalk did not fall from the sky. Nor is this some developer's bright idea for new housing. It is, of course, an art project, by the wildly inventive Sarah Sze, and brought into life via the Public Art Fund. Its official debut is Tuesday, May 2nd, but the installation process took place Thursday, April 27th and will be complete once Con Ed puts in the wiring.

The work is an exact replica (to scale, more or less) of a corner of a building opposite the site on Fifth Avenue, but it also includes a surprise subterranean view into an interior wholly of Sze's imagination. "In a lot of my work there are elements you are used to seeing every day, but then in the context or in the placement of them they have a new life," says Sze, whose intention was always to "go below ground, because when you look up in Manhattan to try and compete with that scale would be so hard. But when you go down, you create a perspective that you are not used to." Click on the slide show to see how it all came together.