Why would a line form around the block?

I see the darndest things out my window. There is currently a line forming that goes all the way down my street block and around the corner onto the avenue. The people are pretty varied, though it seems that most of them are younger. They have no unifying features of dress or anything like that, although a good number have backpacks and other larger bags. The group is racially diverse and the male/female ratio is pretty equal. The line moves in semi-large chunks periodically. I live in the East Village. Do you have any idea of what this line could be for?