Detroit Public Schools Book Depository.

This was featured on boing boing ages ago, but I figure if I missed it, I probably wasn't the only one:

Don't miss this flickr set featuring Detroit's abandoned Book Depository.  There's a blog post about it (with more photos) as well.

As cc (who sent me the first link) said, it's "weirdly beautiful and viscerally sickening at the same time".