above-ground aerial-walkway architectural architecture cables connected connections danger dangerous elevated futuristic Gardens-by-the-Bay height high iconic icons landmarks OCBC-Skyway panoramic panoramic-vistas pedestrians reinforced-concrete safety scenic Singapore skyline steel stroll strolling strong Super-trees Supertree-Grove suspended tree-tops trees vertical-gardens views vistas walkway angle angled angles arial-walkway barrier bridge footbridge higher inclining light mesh metal overpass path patterns pedestrian perspective perspectives protection protective public raised rising safe secure security shadow shadows sloping stable sunlight sunshine support supported tree-top