In case you're new to the city, or maybe this is your first time participating in the race, here's a quick and dirty guide for what to expect.
What is Bay to Breakers?
It's an annual foot race across San Francisco. Most notable for the vivid costumes people wear (or lack of costume in some cases) and dividing the city in half (hence all the tweets about road closures and transit detours, but we'll get to that), the race brings people to the city from far and wide.
According to its website, the first race was held in 1912, and the event has been going strong ever since.
Tens of thousands participate, but even if you aren't running or watching, you'll probably still stumble upon festivities related to the race if you're in San Francisco, so plan accordingly.
The race starts Sunday, May 20 at 8 a.m. with the finish line closing at 1 p.m., but unofficial celebrations can continue well after the route is broken down.
What's the route?
Starting on Howard Street, almost to Embarcadero, the race goes through SoMa, up 9th Street to Hayes Street, along the Panhandle and ends on the western edge of Golden Gate Park. There are multiple water stations and first aid areas set up along the route.
The main route is 12 kilometers (about 7.45 miles), but there is an extra loop set up for people who want to do 15 kilometers (also known 9.32 miles).
There will be closures
City transit agenices have been trying to remind people all week to prepare for this. Though the race is 8 a.m. to 1 p.m., some closures will start Saturday night. If you plan to drive around the city or take public transit, SFMTA has a handy page with lots of links explaining reroutes, closures and more.
For people participating
If you haven't trained yet, there's no real advice to get you ready for the physical aspects of tomorrow's race, but if you find yourself in need of assistance during the race there are plenty of emergency services in place to help.
Staying hydrated (with water, alcohol is banned from the race) is also key, which is why there are many water stations along the route. The end of the race will feature a festival with food, drink and entertainment.
If you have a pet, San Francisco Animal Care and Control recommends you don't bring it to the race since they aren't allowed.
For people not taking part
If you want to cheer on participants (or just want to see the array of costumes) you'll want to claim your spot along the route early.
Though the race is over midday, it can still throw a wrench in plans if you get stuck on the opposite side of the city that you need to be on. Pay attention to the closures listed above before setting out.