San Francisco is considered to be one of the most beautiful cities in the United States. Probably it's even one of the most beautiful places in the world! Anyway, San Francisco is just unique! I have never seen such an awesome place before! Neither have I ever seen any other city so far which has as many sights to offer as San Francisco. There's so much to see and do! I would recommend to stay there for at least 5 days.
Favourite spots:
Golden Gate Bridge, Wisherman's Wharf, Pier 39, Golden Gate Park
What's really great:
the unique architecture (Victorian houses), the sea lions at Pier 39, the sea
Sights:
Golden Gate Bridge, Fisherman's Wharf, Pier 39, Golden Gate Park, China Twon (it's considered to be the largest Chinese community outside China), Union Square
Other recommendations:
Just stroll around the city and have a look at San Francisco's unique architecture; I just loved the Victorian houses.