The scale is overwhelming. It's amazing!
Discussion
The Grand Canyon is also overwhelming. There is a story and Luis and Clark, explorers and surveyors, who saw the Grand Canyon and at the top sent a team down to get water. After half a day the team turned around and reported that the canyon was much bigger than everyone thought.
I've been there, it's the greatest thing I've seen in the US by a long shot. Next time I plan to stay over night at least.