The Farallones are a group of islands about ~27 miles, pretty much due west of the Golden Gate Bridge. They're not huge but you can see them with the naked eye from the top of Mt Diablo about 50 miles away. There's a scientific research station on the largest one but due to their rocky coast (and environmental law) they're difficult or impossible to visit by boat.

Also, part of the City and County of San Francisco!

You can see them with the naked eye from most of the bay area coast, weather/smog permitting. My favorite is Point Reyes.