Riddle #623

Question: My shallow hills are the faces of kings.
My horizon is always near.
My music sends men to the grave.
My absence sends men to work.

What am I?

Question: What fish only swims at night?

Question: What do you call a mad elephant?

Question: What kind of mouse does not eat, drink or even walk?

Question: What has a bed that you can't sleep in?

Question: Where do all the letters sleep?