One cheery, heavyset, tattooed young women stopped me and asked for directions, and for help in re-tying her armband. She pulled me over into an alley; apparently she didn't want to be caught cheating. The situation struck me as comical, and I imagined a police cruiser slowing down for a look at what must have appeared to be a couple of junkies getting a fix.
A few minutes later I ran into a couple of young guys, both equipped with armbands and maps but apparently in less of a hurry than the rest. (I gathered that it was a race of some sort, and wondered if it was a scavenger hunt of the sort they have in Portland.) I stopped them and asked them about it - was it some sort of game? From what I was able to get from them, it was an annual event that had been started a few years ago, and had something to do with zombies.
I gleaned the name "Journey to the End of Night" from the maps, and it turns out the thing is "a free street game of epic proportion run by volunteer masterminds in cities around the world. It is a race/chase through city streets at night." [http://ichaseyou.com/]
OK, so there it is. Well, you never know what you're going to run into when you step outside.