Answer:
What lies in a tunnel of darkness. That can only attack when pulled back?
I'm white, I'm round, but not always around. Sometimes you see me, sometimes you don't.
A beacon from home to guide your way. It can be a lifesaver on a stormy day. What is it?
I have rivers without water. Forests without trees. Mountains without rocks. Towns without houses.
What is it that no man ever yet did see, which never was, but always is to be?
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.