Is Twin Peaks in San Francisco walkable? Can I walk to everything or do I need a car?

Twin Peaks is not really very walkable. It is not so much that things are that far, it is more about the landscape: it is kind of hilly and the streets are made more for cars than people. Also Market has a big divider in the middle of it, so you can only cross at certain points. Unless you really know your way aound, or have the time to figure it out, I would say you need a car. Locals might disaggree.