Clearly, it was an orb weaver's spiderweb covered with hoarfrost. It looked like the crocheted doilies my grandmother made.
Trees, rocks and the water pouring over the falls were obscured by the fog.
As we walked along, we saw webs made by spiders other than the orb weavers. The spider who made this web makes it close to the ground. Then it sits in the hole close to the center and waits for dinner to drop in.
This spider is more of a three-dimensional artist or maybe a spider interested in architecture. The web has walls and a floor.