At practically any hour of the day, you can look at the Sydney Harbour Bridge and see what looks like a procession of ants moving slowly along its vertiginous upper arch (known locally as “the Coathanger”). These are intrepid folks making the famous BridgeClimb, a 3.5-hour guided trek that brings them 440 feet up above the harbor waters. The tours leave four times daily (the dawn and sunset climbs are most popular) and aren’t for everyone; participants should be physically fit enough to do extended “uphill” walking along catwalks and ladders, and—obviously—should be without fear of heights. The good news, though, is that the climb is perfectly safe: everyone is fastened via a safety cable to the bridge struts, so falling is impossible. You won’t be allowed to carry a camera, but your leader will snap your photo at the bridge’s apex.