What am I?

I have keys but no locks. I have space but no room. You can enter but cant go outside. What am I?

Never resting, never still, Silently moving from hill to hill, I do not walk, run or trot, But all is cool where I am not. What am I?

I'm where yesterday follows today and tomorrow is in the middle. What am I?

Always a part. Never a whole. If only half grows I shrink. What am I?

Riddles and Answers