The San Francisco Marathon
An iconic run, but nowadays only the marathon distance goes over the Golden Gate Bridge.
This was my first marathon, in 2009, and I loved running over the Golden Gate Bridge and through the Golden Gate Park. It was quite hilly, especially after the Park, and quite a lot of people walked the hills. It's a big race so there are plenty of supporters and they can spectate from multiple places by hopping around on a dedicated shuttle bus. San Francisco's weather is notoriously fickle, so you may not get to see any scenery at all if the fog rolls in. I started with light fog that soon lifted to an overcast sky, which remained until the sun broke through a few miles from the end. It quickly heated up at that point, so looking back I think it was pretty ideal weather for a first-timer.