Answer:
Face with a tree, skin like the sea. A great beast I am. Yet vermin frightens me.
As soft as silk, as white as milk, as bitter as gall, a thick green wall, and a green coat covers me all.
I can sizzle like bacon, I am made with an egg. I have plenty of backbone, but lack a good leg. I peel layers like onions, but still remain whole. I can be long, like a flagpole, yet fit in a hole.
What word looks the same upside down and backwards?
I am the hole in the night, the ever watchful eye. I return in a cycle, to enlighten the sky.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.