The 440-foot (134 m) Harbour Bridge, the world's largest steel-arch bridge, may be viewed from afar or from the top. BridgeClimb, begun in 1998, offers small-group climbs via catwalks, stairways and ladders leaving every 10 minutes. All the way to the top (almost four hours) or half way up (1.5 hours), the view is like no other. Only moderate fitness is needed, but hardier souls taking fewer stops and keeping up the pace can do the full climb in 2.25 hours. Day, night and twilight tours are offered.