Answer:
Without a bridle, or a saddle, across a thing I ride a-straddle. And those I ride, by help of me, though almost blind, are made to see.
Vikings use this for warmth.
In the night a mountain, in the morning a meadow.
You get many of me, but never enough. After the last one, your life soon will snuff. You may have one of me but one day a year, When the last one is gone, your life disappears.
Many have heard it, but nobody has ever seen it. It will not speak until spoken to. What is it?
People take me on walks and I run and have fun. What am I?