Over the past couple of weeks, you may have seen more people than usual walking erratically, stopping suddenly, all while clutching a smartphone. They were probably playing Pokémon Go, the game that raised a big wodge of cash last year; it launched last week and has gone thoroughly viral in the meantime.

The Facebook event for a San Francisco Pokémon Go crawl tonight (July 20th) has 8,800 people confirmed in attendance, with another 29K “interested” in the event and an additional 12K people invited. Yowzers!

“I had no idea that this event would reach such a large scope of people. I made this event at midnight, invited my facebook friends, and fell asleep,” the organizer of the Facebook event, Sara Witsch, tells me. “I woke up to 500 people going. Within 24 hours, it reached 2k going and 11k interested. I only expected maybe a few hundred at most, if anyone at all.”

“Saw a crawl for Sacramento and thought hey, what better place than a crawl in San Francisco,” Witsch wrote on the Facebook event page, not realizing what was about to happen.

The group came to life with suggestions of dressing up as your favorite Pokémon for the crawl. The event is set to start as a stroll through the city, before culminating in a bar crawl. It’ll be one hell of an overspill at even the biggest bars, however, if even a fraction of the respondents turn up.

“I’m working on a route that will take in consideration the amount of people RSVPed as going and as interested,” she tells me. “The plan is to make multiple break-off points based on neighborhoods so that people can follow the route as far as they’d like, but also so that we don’t have thousands of people in one spot.”

If the app still makes no sense to you whatsoever and you have no idea what the fuss is all about, perhaps the explainer video from the Pokémon Company will help:

I reached out SFPD and will update the story when I get a reply.

UPDATED: I spoke with the event organizer and added her comments in the article above.

UPDATED: The story was updated with the most recent numbers on the same day of the event.