Ok, my response was a lil too harsh, so to make up for it, I did a google search and found this information which might help you:

http://www.travelchinaguide.com/embassy/visa/free-72hour/

So it says, beginning this year, they instituted no visa policy for 72 hours in Beijing and Shanghai for travellers with passport from 45 countries including USA. This probably means if your passport is Nepali then you will need a visa to go outside.