Answer:
I am round as a bowl, deep as a tub, but all the world's water couldn't fill me up.
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.
What instrument can make any sound and be heart, but not touched or seen?
I am the red tongue of the earth, that buries cities.
What can be heard and caught but never seen?
I saw the dead bring forth the living. I saw the living bring forth the dead. What did I see?