I am traveling from San Francisco to Mumbai via Zurich Airport, where I have 18hrs halt. I have an Indian Passport and a valid US F1 visa.
Can I leave the airport and do some sightseeing in Zurich?
No, you cannot. As an Indian citizen, you can transit in Zurich without visa under certain conditions but you need a proper Schengen visa to leave the airport. There are no exemptions or visa-on-arrival for short visits or sight-seeing during layovers in the Schengen area. If you want to do that, you need to go through the whole rigmarole (providing various documents, paying the fee, having your biometrics taken, etc.)