City sightseeing buses (Sydney) run on two routes. The first is known as the 'Red Route'. It leaves Circular Quay and drives within the streets of the city. Some of the stops on this route include;
Circular Quay (Alfred Street)
Town Hall (Queen Victoria Building)
Sydney Opera House
The second bus route is known as the 'Blue Route'. It travels from Central Railway Station to Bondi Beach via Chinatown and Sydney Tower and then circles back to the city via Rose Bay and Double Bay before the tour ends at the Australian Museum.
A third route also runs outside of Sydney in the Blue Mountains where you can hop off at Scenicworld and ride the cable cars. Or you can gaze at the Three Sisters. .
City Sightseeing Blue Mountains (Creative Commons).