Grand Canyon National Park (Arizona)
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1 Day is not enough to cover the whole Grand Canyon. That is a guarantee. You might be able to see 1 of the Rims for a good length of time, but unless you are very quick to judge and consider yourself a very casual observer, then you will probably need a couple of days to see the Grand Canyon from at least the South & West Rims, then, if possible, explore the Canynon in a more up-close & in-depth manner with a hike down the. There are also other options in seeing the Canyon, ie. helicopter tours, Native Indian guides, etc.
With the new Skywalk, this natural wonder will not soon be forgotten.