My int'l friends are visiting me next week. unique and interesting sightseeing tips appreciated.

Three of my friends from Korea are coming up to SF next week to visit me. I was their English teacher back in Seoul. They have been studying photography in Pasadena for the past few months.

I can take them to see the bridge, the park, etcetcetc...but more than that, I'd like to show them some secrets and unique stuff about SF. I don't know SF well (I live in the East Bay), so some suggestions would be appreciated. I figured Reddit would be a good place to get insider info. Also, please don't limit your suggestions just to SF -- East and South Bay also have a lot of gems I'm sure.

They're a bit conservative, so places like Power Exchange are out of the question.