You can pay (lots of money) to climb the bridge and we saw people doing that. We opted for the free version of just walking on the bridge. I don't know what the views are like on top, but they were great from where we were, even in less than ideal weather.
Since we were staying in Woolloomooloo we got to the bridge by walking through the botanical gardens down by the opera house and then up to Circular Quay. Circular Quay is the main ferry terminal. We’ll get back to that — literally — later. Like Waikiki, Sydney had volunteers on hand to help guide visitors. One of these kind ladies pointed us toward the elevators that would take us up to the raised road that crosses the end of the Quay. We walked across that to the other side of the ferry terminal and the bridge.
It’s a nice easy walk though surprisingly long to get around the Quay to the bridge.
You can only walk on one side of the bridge, the side that the opera house is on.