Millions of visitors a year come to Arizona's Grand Canyon National Park, one of the seven natural wonders of the world and the most visited national park in the western United States. However, on extremely rare days when cold air is trapped in the canyon and topped by a layer of warm air, which in combination with moisture and condensation, form the phenomenon referred to as the full cloud inversion. In what resembles something between ocean waves and fast clouds, Grand Canyon is completely obscured by fog, making the visitors feel as if they are walking on clouds.
