Answer:
In marble halls as white as milk, lined with a skin as soft as silk. Within a fountain crystal-clear. A golden apple doth appear. No doors there are to this stronghold, yet thieves break in and steal the gold.
A precious fluid, thicker than water.
The root tops the trunk on this backward thing, that grows in the winter and dies in the spring.
The ones who see it may go blind, Contracting the fool's madness. You have to dig to find it, Crush big stones or mine it. Wash dirt clumps in a pan and wait for it to settle, A shiny, precious metal.
Three lives have I. Gentle enough to soothe the skin. Light enough to caress the sky. Hard enough to crack rocks.
The warmer I am the fresher I am.