In Journey to the Center of the Earth, the explorers, after being trapped in a dark tunnel, emerge into a huge cavern. Above, a granite ceiling soars far away. The area is lit by what Axel describes as natural electricity, and with this light, the explorers can see a vast lake stretching in every direction.
After that, Axel finds what he describes as a "lofty forest." The trees are tall and "tufted" at top. Their tops are shaped like "parasols." They are perfectly still, as if "petrified." Axel is stunned at these trees and filled with admiration of them. His uncle, Otto, coolly informs him that they are giant mushrooms. Axel sees that Otto is right: he is confronting a forest of white mushrooms forty feet high.
It makes sense that mushrooms, plants that on the surface of the planet thrive in shady, forested areas, would grow in the dimmer, more diffuse light near the planet's core.
The whole scene unfolding—the vast, untouched lake, the mushroom forest, and later, a forest of trees like those on the earth's surface—fills Axel with a sense of wonder. He describes the sensation as comparable to how one might feel being the first to land on a new planet where no one has ever set foot.