We have a 4 hour layover! Anywhere to stretch our legs nearby?
4 hrs is barely enough time to get off your flight to go to the next flight, not enough time to get off the airport.
There are often some interesting exhibits at SFO. I agree you don't have enough time to leave the airport.
There's a medium-sized mall called the Tanforan Mall one BART stop away from the airport. You should have time to roam around in there for 90 minutes or 2 hours. There's nothing special about the mall, though. It's just your typical mall.
Or you can go to downtown Burlingame for an hour or two. You'd have to take a cab/Lyft/Uber.
Thanks for the great suggestions. We went down to the Bay Bridge and walked along the path. Also, checked out a funky art piece/ fountain and.c artists' market nearby. It was a quick out and back using the BART which is a great subway system. I definitely want to come back to SF.
Cool city with friendly people.