If you stay near Union Square you'll have about a 15- to 20-minute run from your hotel to what I consider runnable areas.
But, given that's your starting point, the obvious route is to take Market St. east to the Ferry Building and then follow the Embarcadero. Which you can follow as long as you want, really -- all the way to the bridge, in fact. Round trip, that's about a 11- or 12-mile out-and-back, but of course shorten it as you see fit.
Your second option from a Union Square starting point is west through the city. You should aim to hit the Panhandle and then from there run through Golden Gate Park, to the ocean if you're up for a run of that length. Pause for a moment or two on the beach to soak it in -- enjoy the view!
I agree with the above poster: If you can get out of the city proper -- either north to Marin or south to the Santa Cruz mountains -- you'll have a wealth of great routes to consider.
I have no input on where to run a track workout.