Answer:
I can move even when you are still. I can be one or many.
You saw me where I never was and where I could not be. And yet within that very place, my face you often see.
Two horses, swiftest traveling, harnessed in a pair, and grazing ever in places. Distant from them.
It's usually found dried, but often kept slicker. Above another need, it's said to be thicker. What is it?
A great mysterious place that the bold have been known to journey into.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.