Grand Canyon South Kaibab to Skeleton Point section is the longest hike recommended for day hikers. The out and back route has a vertical of 610 meters (starting at almost 2200m); the hot, exposed trail adds to the difficulty.
We got a fairly early start so it was quite cool; but that quickly changed when the sun hit the trail -- 10° C (50°F) became 35°C (95°F) in about ninety minutes. This was early October. There's a sign along the way that states "Going down is optional -- going up is mandatory"; a point that can't be stressed enough. We started with 3 liters of water each and returned empty.
Off of Yaki Point Road 36°03'10.6"N 112°05'02.2"W -- during peak seasons you'll have to take a shuttle bus.
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