What leads Neo to believe he needs to go to the Machine City?
Several things combine to help him draw this conclusion. He knows now that his fight is not with the machines, it’s with Smith. Smith is the greater threat to Zion, humanity, and the Matrix. He’s also seen visions of the real world leading him to the city. He’s also beginning to believe peace can be brokered, as opposed to won through force. He has to go to the Source (where the path of the One ends) and try to make a deal for peace.