In Dragon Ascending, the first book of the Vanir Dragon Series, we catch a brief view of the Firefall at the Edge of the World. This phenomenon happens for only a few days before and after the summer solstice and can be seen only from the Vanahir side of the Crevasse.
At sunset near the solstice, the golden light of the setting sun shines down the channel between the great islands Vanahir and Faehold all the way to the Edge of the World. When the angle is just right, the light passes through the thin curtain of the waterfall and reflects off the rocks behind it, passing back through the water and making it glow like fire.
This fictional phenomenon was inspired by the real-life "firefall" effect that happens at Horsetail Falls in Yosemite National Park (a much smaller waterfall than the Edge of the World) for the last two weeks of February. When conditions are just right, the sunset light reflects off the rocks, causing the waterfall to glow like fire.
The video below provides additional information about this natural wonder.
Video courtesy of the U.S. National Park Service. [Public Domain]